Abiogenic. Describes anything formed through nonliving processes.

Accommodation space. Sediments can be deposited only where there is somewhere for them to accumulate. Subsidence or other processes that produce a trap for sediments are said to produce accommodation space.

Accretionary wedge. The mass of sediments scraped off a subducting slab and accreted to the overriding slab in a destructive plate margin.

Acritarchs. An extinct family of tiny organisms that may be among the earliest eukaryotes.

Aeromagnetic Survey. The measurement of magnetic fields above the earth's surface by low-flying aircraft. Originally developed to detect ore bodies, it can also trace basement structures hidden below nonmagnetic sedimentary beds.

Age Control. A feature in a sequence of rock beds that establishes either a maximum or minimum age for the bed. Age controls include direct dating of volcanic beds and indirect dating by correlation of fossils contained in the bed.

Alkaline. Used to describe igneous rocks that are unusually rich in sodium or potassium. Not all the alkali metal can be incorporated into feldspar, so less common silica-rich minerals form, such as feldspathoids.

Alluvial Fan. A deposit of sediments shaped like a section of a shallow cone, with the tip of the cone at a source of sediments. This is often a canyon emerging from a mountain front. Alluvial fans vary in size from a few meters to hundreds of kilometers across, and form distinctive sedimentary formations in the geologic record.

Alpha Decay. A form of radioactive decay in which an unstable atomic nucleus emits two protons and two neutrons in the form of a helium nucleus.

Amphibole. A family of double chain inosilicate minerals common in igneous rocks, containing water in their structure.

Andesite. An intermediate extrusive igneous rock, found extensively in the southern Jemez.

Angular Unconformity. An unconformity in which the formations above the unconformity lie at an angle to those below.

Anion. An atom or group of bonded atoms that has picked up one or more extra electrons, so that it has a net negative electrical charge.

Anorogenic. Not associated with an episode of mountain building. Used to describe certain granites or other rock formations.

Aphanitic. Colmposed of crystals too small to be seen with the unaided eye.

Archean. The second eon of the earth's geological history, from 4 billion to 2.5 billion years ago.

Arenite. A sandstone containing less than 15% clay minerals in its pore spaces.

Arkose. A sandstone containing more than 25% feldspar clasts.

Ash. In geology, a fine powder of very small rock fragments (less than 2mm in size) produced by violent high-silica volcanism.

Asthenosphere. A region in the upper mantle, starting about 50 miles down but with no sharp lower boundary, where the rock is very close to its melting point and is relatively easily deformed. Pockets of magma are likely present in some parts of the aesthenosphere.

Back-Arc Basin. A small ocean basin that forms on the landward side of some destructive margins.

Banded Iron Formation. A rock consisting of alternating layers of silica and iron oxides, formed under water in conditions that existed only in Precambrian time.

Basalt. The most common extrusive mafic rock, found extensively in the Jemez area. Usually black to light gray in appearance.

Basaltic Andesite. A rock intermediate between basalt and andesite.

Basanite. An  ultramafic alkalic extrusive rock with a low enough silica content that little feldspar is present. Typically consists of a mixture of clinopyroxene, nepheline, magnetite, and olivine.

Batholith. An immense body of plutonic rock covering up to hundreds of square miles and extending deep into the crust. Batholiths typically occur in old sutures and subduction zones.

Bentonite. A form of clay rich in montmorillonite that typically forms from weathered volcanic ash.

Beta Decay. A form of radioactive decay in which an unstable atomic nucleus emits an electron and an antineutrino, which transforms one of the neutrons in the nucleus into a proton.

Bimodal. In the broadest sense, refers to any statistical distribution with two distinct peaks. In geology, usually refers to a volcanic center where high silica and low silica rocks are present with little intermediate silica lava.

Biogenic. Describe anything produced by the activities of living organisms.

Biotite. An iron-rich mica mineral.

Bioturbation. Disturbance of a sedimentary bed by the activities of living organisms shortly after the bed was laid down.

Birefringence. An optical property of certain minerals, which causes images seen through the mineral to be doubled. Calcite is the most common mineral showing this property.

Block And Ash Flow. A pyroclastic flow consisting of a large volume of lithic fragments embedded in ash of similar composition. Typically formed when part of a dome or high-aspect flow of high-silica lava collapses.

Breccia. A sedimentary rock containing broken, irregular clasts over 2mm in size.

Calcium-aluminum inclusions. Fragments of material found in the most primitive meteorites that are believed to be the oldest solid substances in the Solar System.

Calc-alkaline. Describes a suite of igneous rocksmoderately enriched in the alkali metals, potassium and sodium, and the alkaline earths, calcium and magnesium. Other distinctive chemical characteristics include a high aluminum content and a tendency to steadily decrease in iron content as the silica content increases.

Caldera. A large bowl-shaped depression in the Earth's surface, typically produced by a massive volcanic eruption that empties an underground magma chamber whose roof then collapses.

Cambrian. The epoch from 540 to 485 million years ago. There are no formations of this age in the Jemez area.

Carbonaceous Chondrites. A type of very primitive meteorite that is virtually unchanged from the time the Solar System formed. Carbonaceous chondrites give us some of our best information on the age of the solar system and conditions at its beginnings.

Cation. An atom that has lost one or more electrons, so that it has a net positive electrical charge.

Cement. Minerals deposited in a sedimentary rock by ground water that binds the rock together.

Cenozoic. The present era of the Earth's geological history, from 65 million years ago to the present. It is further subdivided into the Paleogene, Neogene, and Quaternary periods, although the Paleogene and Neogene periods are still often lumped together as the Tertiary.

Chromosomes. Structures containing linear double strands of DNA in eukaryotic nuclei.

Core. The central part of the Earth, beginning about 1800 miles down. Composed mostly of iron with significant quantities of nickel and sulfur. The outer core is liquid while the inner core is solid.

Clast. Geological term for a fragment of rock, of any size from microscopic to as large as a bus, found either loose or cemented into a sedimentary bed.

Clastic Sedimentary Rock. Sedimentary rock composed mostly of broken fragments of rock (clasts) of microscopic size to boulders.

Cleavage. A property of many minerals, which fracture along flat surfaces lying at a characteristic angle to each other.

Complex. A body of rock that has been so distorted, by metamorphism or igneous intrusion, that the chronological order of the beds is difficult to discern. A complex contains mixed rock types, such as sedimentary with volcanic.

Conglomerate. A sedimentary rock containing rounded clasts over 2mm in size.

Consolidated. Describes a sedimentary bed in which the clasts are closely packed together. A consolidated bed is often also well indurated, but this is not always the case.

Contact Metamorphism. Metamorphism due to local heating by a nearby intrusion of magma.

Continental Platform. The portion of a continent consisting of stable crust covered with sedimentary rock.

Continental Shield. The central portion of a continent consisting of stable crust where Precambrian rocks are widely exposed.

Convection.  The process in which liquid or ductile solid material flows from regions of high temperature to regions of low temperature and back, thereby transporting heat energy.

Correlation. The process of matching up rock formations from distant locations that have the same age, either through comparison of fossils or through radioisotope dating.

Country Rock. The surrounding solid rock through which magma passes on its way to the surface. This rock is often quite different in composition from the magma.

Covalent Bond. A bond formed between two (usually nonmetal) atoms when they share one or more  pairs of electrons.

Craton. The stable central part of a continent. This usually consists of a continental shield surrounded by a continental platform.

Cross Bedding. A feature of sedimentary rocks laid down in a strong current. Thick beds are made up of thinner cross beds lying at a steep angle to the main beds.

Crust. The outer layer of the earth, which is about 25 miles thick in the Jemez area. It is high in silica compared with the underlying mantle and less dense.

Curie Temperature. The temperature at which a magnetic substance loses its remanent magnetism and reorients to the ambient magnetic field.

Crystal. A clump of solid material composed of atoms bound together in a regular arrangement. Crystals that have plenty of room in which to form take on a characteristic shape reflecting their internal atomic arrangement.

Cyanobacteria. A large group of chlorophyll-containing bacteria capable of generating oxygen by photosynthesis. Formerly known as blue-green algae.

Cyclosilicate. A mineral built around rings of silicon tetraheda.

Dacite. An intermediate-felsic extrusive igneous rock composed almost entirely of feldspar. If small amounts of quartz are present, it is described as rhyodacite.

Decay chain. A series of radioactive decays that transforms a long-lived radioactive element, such as uranium, to a stable element, such as lead. The first decay usually is much slower than subsequent steps, so that once a uranium atom experiences the first decay in the decay chain, it rapidly continues decaying to lead.

Delamination. A process that may take place at the base of the crust, where a layer rich in iron and magnesium breaks loose and sinks into the underlying mantle.

Deltaic. Describes a sediment deposition environment of a river delta, where a river enters a sea or large lake and abruptly drops its sediments.

Depleted. Describes mantle rock that has had its lowest-melting components already extracted as magma.

Destructive margin. A location where oceanic crust is subducted into the mantle and destroyed.

Diabase. A hypabyssal mafic rock with a very fine salt-and-pepper grainy appearance.

Diagenesis. The process of transformation of a loose bed of sediments into sedimentary rock.

Diapir. A large body of magma deep in the crust or upper mantle that is slowly working its way towards the surface.

Dike. A sheetlike intrusive body that cuts across the bedding of the country rock.

Dike swarm. A system of  many dikes of the same age running parallel to each other.

Diorite. An intermediate intrusive igneous rock, not common in the Jemez.

Dip. The angle a fault plane makes with the surface of the earth, such that a fault plunging straight down into the earth has a dip of 90 degrees.

Dip-slip fault. A fault where the displacement is mostly in the vertical direction.

Discomformity. An unconformity that does not involve any noticeable difference in the inclination of beds above and below the disconformity.

Dolomite. A sedimentary rock rich in magnesium, most likely formed when limestone is exposed to magnesium-rich fluids under the right conditions of temperature, pressure, and oxygen abundance.

Dome. A type of volcanic land form produced by high-silica magma. The interior is viscous magma flowing into the dome from beneath, while the outer layer of the dome is a mantle of solid rock fragments.

Downthrown. Describes the side of a fault in which the beds are lower than on the opposite side of the fault.

Ductile. Having the property of deforming rather than shattering when stressed. Many metals are ductile, while rock becomes ductile at the enormous pressure and elevated temperatures found in the interior of the earth.

Electron Affinity. The "greediness" of a chemical element for electrons. Oxygen has the highest electron affinity of any common element; potassium, the lowest.

Endosymbiosis. A theory of the origin of eukaryotes, in which mitochondria, chloroplasts, and possibly the nucleus began as independent prokaryotes that were taken up into a eukaryotic cell.

Eolian. Describes a sedimentary rock laid down by wind as sand dunes.

Eon. The largest division of geological time. The recognized eons are the Hadean, Archaean, Proterozoic, and Phanerozoic.

Epicontinental Sea.  A shallow sea covering continental crust. The North Sea is a modern epicontinental sea.

Eukaryotes. One of the three main domains of life. Eukaryotic cells have true nuclei and a complex internal structure. They include modern plants, animals, and fungi.

Eutectic. The unique composition of the magma that forms from a particular mixture of minerals at the solidus temperature.

Exhumation. The process of bringing deeply buried rock to the surface as a result of tectonic forces.

Extrusive. Describes an igneous rock that cools on the surface of the earth and, as a result, is glassy or has very small crystals, difficult to see even with a magnifier.

Facies. A body of rock formed in a specific manner in a specific environment. It is common for there to be multiple facies within a given formation.

Fault. A fracture in the brittle upper crust of the earth, with the beds on either side displaced from each other.

Fault Trace. The intersection of a fault with the surface of the earth.

Feldspar. A family of tektosilicate minerals, all having the same basic crystal structure, that form from silica-rich magma that also contains alumina and sodium, potassium, or calcium oxide. Feldspar is very common in igneous rocks and makes up the bulk of the earth's crust.

Feldspathic schist. A form of metamorphic rock rich in feldspar and quartz.

Feldspathoid. A family of silica-poor minerals that form in preference to feldspars from magma low in silica and high in alkali metals.

Felsic. Describes an igneous rock with a high silica content in excess 70%. The word felsic was coined to reflect the high content of FELdspar and SIlica in these rocks.

Ferric Iron. Iron that has contributed three electrons to the compounds it forms, characteristic of high-oxygen environments.

Ferrous Iron. Iron that has contributed two electrons to the compounds it forms, characteristic of low-oxygen environments.

Fertile. Rock that has a low solidus, so that it produces magma with the addition of a relatively small amount of heat.

Fining Sequence. A sequence of sedimentary beds that becomes progressively more fine-grained in the younger beds.

Fissile. Describes a rock, such as shale, that easily splits into thin layers.

Fluvial. Describes a sedimentary rock laid down in a river environment.

Foliated. Describes a rock in which individual mineral grains are aligned. Characteristic of metamorphic rock.

Footwall. The lower side of a fault.

Foreland Basin. A region of subsidence that accompanies an orogen, typically extending for hundreds of miles inland of the mountain front.

Formation. A body of rock that was produced by a particular set of geologic processes over a relatively short period of time. Formations are combined into groups, and subdivided into members.

Friable. A sedimentary bed in which the clasts are so poorly cemented that the sediments crumble to the touch.

Gabbro. An intrusive mafic rock composed of relatively large crystals of plagioclase and pyroxene.

Glacial Till. A distinctive mixture of angular clasts and silt deposited by glaciers.

Glass. In geology, a solidified magma that cooled too quickly to form crystals. The structure is disorganized even at the atomic level.

Gneiss. A high-grade metamorphic rock that typically shows prominent foliation.

Gondwanaland. An ancient large continent incorporating most of what are now the southern continents, South America, Africa, Australia, and Antarctica. Formed in the early Paleozoic and merged into Pangaea in the late Paleozoic.

Graben. A block of crust that has dropped below the surrounding crust (horsts)  along bounding faults.

Granite. A felsic intrusive rock containing large quantities of quartz, found in the Siera Nacimiento Mountains just west of the Jemez and likely present below the surface within the Jemez.

Granodiorite. An intermediate-felsic intrusive rock containing modest amounts of quartz.

Greenstone belt. A region of mafic metamorphic rock interpreted as part of an island arc that was fused to a continental craton.

Group. A set of formations found in the same area representing a more or less continuous span of the rock record. Groups are further divided into formations.

Guard cells. A pair of cells surrounding a stomata, which act to open or close the stomata to control water loss.

Hadean. The first eon of the earth's geological history, from its formation to 4 billion years ago.

Half-life. The period of time in which half of a sample of a particular unstable isotope will experience radioactive decay.

Hanging wall. The upper side of a fault.

Hartzburgite. A rare rock type sometimes found as xenoliths in lava flows. It is believed to be the solid residue left when mantle rock is partially melted.

Hematite. Ferric iron oxide, Fe2O3. Widespread as a cementing mineral in sedimentary rocks. Large deposits of concentrated hematite are one of the most important ores of iron.

Hiatus. A pause in the deposition of sediments in a region.

Hornblende. A generic term for a black iron-bearing amphibole of variable composition, common in igneous rocks.

Hornfels. A very tough metamorphic rock formed from sedimentary rock metamorphosed by the heat of a nearby magma intrusion.

Horst. A block of relatively elevated crust bounding one side of a graben.

Hot spot. A localized region in the mantle, also called a mantle plume, where heat flow to the surface is unusually high. As tectonic plates move over a hot spot, a succession of volcanoes form over the hot spot, leaving a trail of increasingly old volcanoes in the opposite direction from the plate motion.

Hydrated subduction zone scar. A zone along a suture where part of a subducting slab remains in place in the lower crust and upper mantle. The rock in this slab is rich in hydrous minerals, making it fertile for production of magma.

Hypabyssal. Describes an igneous rock that cools just under the surface of the earth and, as a result, is composed of fairly small crystals.

Ichnofossils. Traces left by the activities of organisms rather than the remains of the organisms themselves. These include things like dinosaur footprints or worm burrows.

Iddingsite. A mixture of iron oxides and hydroxides with some clay and silica formed by decomposition of olivine under surface conditions.

Igneous. Describes a rock that forms from solidifying magma, either on or beneath the surface of the earth.

Igneous suite. Families of igneous rocks having a similar origin. Each suite comes from its own distinctive source rock subject to a particular degree and type of partial melting.

Illite. A clay mineral similar to muscovite in composition and structure.

Incompatible Element. A chemical element that is not easily incorporated into common silicate minerals, either because its ions have the wrong size or the wrong charge. Incompatible elements tend to be concentrated in magma when it is produced by partial melting of source rock, and to be further concentrated in the last fraction of the magma to solidify.

Index Fossil. A fossil species with distinctive characteristics that appears suddenly in the fossil record at a precise point in time, allowing a sequence of beds to be dated from its appearance. Index fossils are now used to define the starting poiint of most time intervals in the geologic time scale.

Index Mineral. A mineral characteristic of a certain maximum pressure and temperature of metamorphosis of a rock bed.

Indurated. A sedimentary bed in which the rock has been hardened by the deposition of mineral cement.

Inosilicate. A mineral built around a backbone of long chains of silicon tetrahedra.

Interglacial. A period of relative warmth during an ice age, in which glaciers retreat. We are living in an interglacial today.

Intermediate. Describes an igneous rock with an intermediate silica content of 52-63%. Examples are andesite and diorite.

Intermediate-felsic. Describes an igneous rock having a composition of 63%-69% silica, between that of intermediate and felsic rocks.

Intrusive. Describes an igneous rock that crystallized slowly underground, so that it is formed of visible crystals.

Intrusive Body. A body of plutonic rock, formed when magma forced its way through country rock and then solidified.

Ionic Bond. A bond formed  when an electron is transferred from a metal atom to a nonmetal atom. Because this leaves the metal atom with a positive charge and the nonmetal atom with a negative charge, the two atoms are attracted to each other by the resulting electrostatic force.

Island Arc. A line of volcanic islands formed along a destructive margin above the subducting oceanic plate.

Isostacy. The balance of buoyant forces in the Earth's crust, which causes mountains to form over low-density rock to balance its buoyancy, or crust to subside under ice sheets.

Isotope. A nucleus of a particular chemical element (as determined by the number of protons) with a particular number of neutrons. For example, all isotopes of oxygen contain eight protons, but 16O and 18O are isotopes of oxygen whose nuclei contain eight neutrons or ten neutrons respectively. The total number of protons is specified by the chemical element symbol (O) and the total number of neutrons plus protons by the superscript number.

Isotope Model Age. The age at which a block of crust first separated from the mantle. It remains unchanged even if the block is recrystallized completely, resetting other radiometric clocks.

Jemez Lineament. A zone of enhanced volcanic activity reaching at from central Arizona to northeastern New Mexico. Believed to mark the suture between two Precambrian plates.

Juvenile. Indicates material extracted from the mantle rather than from the overlying crust.

Kaolinite. A clay mineral formed by strong weathering of illite.

Karst Topography. A distinctive kind of terrain that develops on limestone beds in wet climates, where dissolution of the limestone forms caves and sink holes.

Komatiite. A form of ultramafic igneous rock with an extraordinarily high magnesium content, not erupted since the Archean Eon.

Kyanite. A form of aluminum silicate that crystallizes at relatively low temperature and high pressure.

Lacustrine. Associated with lakes, such as lacustrine sediments deposited in a lake bed.

Lamprophyre. A rare igneous rock low in silica and very high in potassium thought to be formed by very slight melting of the upper mantle.

Landslide Scarp. A concave surface on an unstable slope marking the surface where a landslide detached from the slope.

Lapilli. Rock fragments produced by volcanic activity that are between 2mm and 64mm in size.

Large Igneous Province. A region of flood basalts erupted within a relatively short geologic time span and covering a vast surface area.

Lava. Magma that has reached the surface of the Earth still in a liquid state.

Leucosome. The portion of a migmatite that is thought to have melted. Usually lighter in color.

Limestone. A sedimentary rock composed mostly of calcium carbonate, usually formed by deposition of small bits of shells of marine organisms.

Liquidus. The temperature at which a magma first begins to crystallize. Above the liquidus temperature, the magma is completely melted; at or below the liquidus, the magma is at least partially solidified.

Lithological discontinuity. A line dividing areas where the rock beds show distinctive features, such as composition, age, or isotope ratios.

Lithosphere. The outer rigid shell of the earth, consisting of the crust and uppermost mantle. The lithosphere averages about 80 km (50 miles) in thickness.

Mafic. Describes an igneous rock with a relatively low silica content of 45-52%. The word mafic was coined to reflect the high MAgnesium and Ferrous oxide content of these rocks. Examples are basalt and gabbro.

Magma. Molten rock, composed mostly of a mixture of silica and metal oxides with dissolved gases, such as water vapor and carbon dioxide. Magma that reaches the surface still in a liquid state is known as lava.

Magma Differentiation. The process whereby a cooling magma changes in composition as various minerals crystallize out of the magma.

Magnetite. An iron mineral with the composition Fe3O4 that is present in small quantities in many silica-poor igneous rocks.

Mantle. The portion of the earth that begins about 25 miles below the surface in the Jemez area and extends to the earth's core, 1800 miles deep. It is composed of ultramafic rock and makes up most of the volume of the Earth.

Mantle Plume. An upwelling from deep in the mantle that creates a hot spot on the overlying crust.

Mantle Wedge. A wedge of mantle above subducting lithosphere.

Mantle Wedge. A wedge-shaped region of mantle found at a destructive margin, between the overriding plate and the subducting plate.

Mass Extinction. A point in the fossil record where a significant fraction of families of living organisms abruptly disappear.

Matrix. Fine-grained material filling space between much larger clasts in a sedimentary rock.

Mature. Describes a sandstone consisting of almost pure well-rounded, well-sorted grains of quartz.

Megathrust earthquake. An earthquake produced at a destructive margin when overriding continental lithosphere and subducting oceanic lithosphere that have locked together suddenly break loose. Megathrust earthquakes can release stress over a region hundreds of kilometers long to produced the most powerful known earthquakes.

Medial Graben. A graben that forms across a resurgent dome or other area of uplift, caused by the stretching of the rock beds as they are pushed up.

Melange. A unit of highly broken and deformed rock formed by accretion along a destructive plate margin.

Melanosome. The portion of a migmatite that is thought to have remained solid. Usually dark in color.

Member. A part of a formation that is in some way distinguishable from the rest of the formation, even though it was formed in a similar way. For example, the Bandelier Tuff Formation is subdivided into the Tshirege and the Otowi Members, corresponding to two similar caldera eruptions separated by 400,000 years in time.

Mesozoic. The second era of the Phanerozoic Eon, from 250 million to 65 million years ago. It is further subdivided into the Triassic, Jurassic, and Cretaceous periods.

Meta-. Prefix used to indicate the origin of a low-grade metamorphic rock. Thus, a metarhyolite is a metamorphosed rhyolite, a metaconglomerate is a metamorphosed conglomerate, and so on. 

Metamorphic. Rock that has been altered by heat and pressure deep in the earth's crust without actually melting.

Metamorphic facies. A distinctive collection of minerals characterizing metamorphic rock that formed within a particular range of pressure and temperature.

Metasomatism. Change in the composition of a body of rock from fluids from a nearby magma intrusion.

Mica. A phyllosilicate mineral composed of triple layers, each having two phyllosilicate sheets bound together by a layer of metal and hydroxyl and each triple layer bound more loosely to its neighbors by potassium or calcium ions. All micas have a single perfect cleavage plane parallel to the triple layers.

MIcrocline. A feldspar with the composition (K2O)(Al2O3)6(SiO2), stable at low temperatures.

Microcontinent. A small fragment of continental crust separated from the larger continents. A few microcontinents are known today, but they were probably numerous during the Archaean and early Proterozoic Eons.

Mid-Ocean Ridge. A place where oceanic crust is being pulled apart by convection in the mantle, causing mantle rocks to melt and the magma to rise to form new oceanic crust on the axis of the ridge.

Migmatite. A rock consisting of layers of dark (melanosome) and light (leucosome) minerals with a characteristic pattern, thought to represent a rock that was once partially melted deep underground.

Mineral. A substance composed of crystals with a characteristic composition and structure.

Miogeocline. The region of sediment accumulation along a passive continental crust following rifting.

Mohorovičić discontinuity. The seismic discontinuity that defines the boundary between the crust and mantle. Often referred to in the English-speaking world as the Moho.

Molecular Fossils. Organic compounds found in geological formations that point to the existence of certain forms of life when the formation was deposited.

Monogenetic. Describes a volcanic field consisting of numerous small vents erupting mafic magma, where each vent erupts only a few times.

Montmorillonite. A clay mineral formed by weathering of plagioclase feldspar.

Mountain Collapse. When a mountain range is formed by compression, subsequent release of the compression causes the thick crust of the range to spread out.

Mudflow. A gravity

Mudstone. A sedimentary rock formed mostly of clasts of all sizes below 0.0625 mm.

Muscovite. A form of mica with the composition KAl2(AlSi3O10)(OH)2.

Nepheline. A silica-poor feldspathoid mineral with the composition 3(Na2O)(K2O)4(Al2O3)8(SiO2).

Nesosilicate. A silicate mineral containing isolated silica tetraheda, not joined to any other silica tetrahedra.

Normal fault. A fault in which the hanging wall is the downthrown side of the fault.

Oblique-slip fault. A fault where the displacement shows significant displacement in both the vertical and horizontal directions.

Oceanic Island Arc. An island arc formed where oceanic crust is subducting under oceanic rather than continental crust.

Olivine. A nesosilicate mineral with a composition ranging from Fe2SiO4 to Mg2SiO4. Olivine is the most abundant mineral in the upper mantle and is often found in low-silica volcanic rocks at the surface.

Onlap. A set of beds near the geographical limit of a sedimentary formation where the younger beds extend further over the underlying formations than the older beds. Usually indicates subsidence in the region when the beds were laid down.

Opalized. Describes a sedimentary rock in which so much amorphous silica has been deposited that the rock has become highly indurated.

Ophiolite. A slice of oceanic crust (and sometimes the underlying mantle) that was incorporated into a continent, often during closure of a back-arc basin.

Orogeny. An episode of mountain building in the geologic record. Usually associated with the collision of continents. This produces a belt of mountains underlain by deformed rock called an orogen.

Ostracod. Also called seed shrimp. Small crustaceans whose bodies are protected by a clam-like shell.

Paleomagnetism. The study of magnetic fields of ancient rock beds, which give clues to the location of the beds relative to the magnetic poles when the beds were formed.

Paleosol. A fossil soil.

Paleotopography. The geography of an area at some point in the distant past.

Paleozoic. The first era of the Phanerozoic Eon, dating from 540 million years ago to 250 million years ago. It is further divided into the Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, and Permian periods.

Partial Melting. Production of magma through melting of only a modest percentage of the mass of a source rock.

Passive Margin. A continental margin that is not moving relative to the offshore oceanic plate, so that no particular seismic or volcanic activity takes place.

Pegmatite. A very coarse-grained plutonic rock, usually very rich in silica and incompatible elements.

Pelitic. Describes sedimentary rock rich in clay minerals, or metamorphic rocks transformed from clay-rich sedimentary rock.

Peneplain. A very flat surface produced by extended erosion during a time of tectonic stability.

Peraluminous. Describes a rock containing more aluminum than can be incorporated in feldspar, so that mica or more unusual aluminum-rich minerals are present.

Perthitic. Describes microcline or orthoclase in which sodium and potassium have separated into very fine layers, visible with magnification or sometimes with close examination.

Phanerozoic. The present eon of the Earth's geological history, from 540 million years ago to the present. Further divided into the Paleozoic, Mesozoic, and Cenozoic Eras.

Phase Change. A change in the physical structure of a substance that does not involve any change in composition. Ice melting to water is a phase change. Minerals often experience phase changes from one solid structure to a more compact solid structure as the pressure increases deep in the Earth.

Phenocryst. A relatively large mineral crystal embedded in a mass of much finer crystals (the ground mass). Phenocrysts typically form before the magma is erupted as lava.

Phyllosilicate. A silicate mineral whose backbone is sheets of silica tetrahedra joined to neighboring tetraheda at just three of their four corners.

Picritic Basalt. A very low-silica basalt characterized by abundant olivine phenocrysts but without elevated alkali content. Quite rare in continental settings and not found in the Jemez.

Pilllow Basalt. Basalt with a distinctive lobate structure indicating it was erupted in deep water.

Pinching Out. Describes where a formation thins to a knife edge and disappears, leaving the beds above and below in direct contact.

Plagioclase. A feldspar mineral, varying in composition from CaAl2Si2O8 to NaAlSi3O8, found in a wide range of igneous rocks.

Planetesimal. One of the large bodies that merged to form the planets in the first 10 million years of the Solar System.

Plate. A region of the lithosphere that moves as a single body across the underlying aesthenosphere.

Plate Tectonics. The unifying theory of modern geology, which holds that the crust and upper mantle (the lithosphere) is broken into several large plates that are carried along by currents in the underlying mantle.

Plate flexure. The tendency of continental lithosphere to subside next to an orogen due to the weight of the mountains, producing a foreland basin.

Plutonic. Describes a rock that forms far beneath the earth and, as a result, is formed of large crystals, easily seen without a magnifier.

Polymorph. Two different forms of a mineral, sharing the same composition but differing slightly in structure, that are stable at different ranges of temperature and pressure.

Porphyritic. Describes a rock composed of relatively large crystals (phenocrysts) embedded in a much finer matrix (the ground mass).

Precambrian. The period of geologic time from 4.55 billion to 540 million years ago, in which life on earth was at so primitive a state of development that few fossils are found in rocks of this age.

Primitive magma. The original magma formed by partial melting of source rock, prior to any differentiation or contamination by country rock.

Prokaryote. An organism belonging to the Bacteria or Archaea, two of the three domains of life. Prokayotes have relatively simple cells with no true nucleus or other compartments.

Proterozoic. The third eon of the earth's geological history, from 2.5 billion to 540 million years ago. The oldest rocks in the Jemez area are Proterozoic in age.

Protolith. The original rock from which metamorphic rock has recrystallized.

Province. Used in two overlapping senses. A Precambrian province is a region of crust formed in a single short period of time before being assembled into larger continents, such as the Yavapai Province. A tectonic province is an area of crust characterized by a particular history since its formation, such as the Colorado Plateau.

Pyroclastic flow. A form of volcanic eruption consisting of a flow of extremely hot gas in which fine rock particles are suspended. The rock particles make the flow heavier than air, so that it can move downhill, often at very high speed. When the flow finally comes to rest, the rock particles settle out to form a tuff.

Pyroxene. A family of silica-poor minerals for which a typical composition is (CaO)(FeO)2(SiO2). Often very dark in color from the iron content.

Quartz. A hard mineral formed from pure silica.

Quartzite. A metamorphic rock formed almost entirely of quartz.

Rain Shadow. An arid region downwind of a high mountain range, produced when moisture in the prevailing winds is wrung out of the air over the mountains.

Reaction Rim. A zone of altered compositon around a crystal, such as pyroxene around an olivine crystal, caused by the magma reacting with the crystal during cooling.

Refractory. Describes a solid material that has a very high melting point.

Regional Metamorphism. Metamorphism over a broad region caused by a widespread tectonic event, usually mountain building.

Regression. The retreat of an ocean from off a continent over geological time scales.

Remanent magnetism. The magnetic field of a magnetic substance as determined the last time it cooled below its Curie temperature.

Reverse fault. A fault where the footwall is the downthrown side of the fault.

Rhyodacite. An igneous extrusive rock intermediate in composition between dacite and rhyolite, with significant quartz content.

Rhyolite. A felsic extrusive rock containing significant quantities of quartz, found extensively throughout the Jemez.

Rift Valley. A valley formed by rifting of the crust.

RiftingThe process of crust pulling apart.

Rio Grande Rift. A region running from central Colorado to northern Mexico where the crust is being slowly pulled apart, coinciding roughly with the valley of the Rio Grande.

Roof Pendant. An isolated outcrop of country rock on the exposed surface of a batholith, interpreted as part of the roof of the batholith that has not quite eroded away.

Sand cycling. A process that occurs when river directions are opposite to the prevailing winds. Sediments are repeatedly carried downriver, only to be picked up by prevailing winds and redeposited upriver. This thoroughly winnows and sorts the sediments, producing very mature sandstones.

Sandstone. A sedimentary rock composed mostly of clasts that are 0.0625mm to 2mm in size.

Schistose. Describes a rock that easily splits into thinly laminated layers.

Sedimentary. Describes rock formed from eroded mineral fragments that are cemented together at low temperature and pressure. Differs from metamorphic rock in that the original rock fragments are not significantly altered.

Seismic Discontinuity. A depth in the earth at which seismic wave velocities abruptly change. This indicates either a change in composition or a change in crystal structure with the same composition.

Seismic Profiling. A method for obtaining information about the crust and upper mantle. Sound waves are generated with explosives or heavy weights dropped into a borehole, or using a heavy vibrating plate on the surface of the ground, and their reflection is used to map underground structures. This is analogous to the use of sonar in the oceans.

Shale. A sedimentary rock containing substantial amounts of clay flakes that have lined up in such a way that the rock shows very thin layers that are easily split.

Shallow Marine. Describes a sedimentary rock deposited in relatively shallow ocean water, such as on a continental shelf.

Shatter Cone. A distinctive pattern of fractures in otherwise solid rock that is produced only by a violent shock wave, as from an underground nuclear detonation or a major impact event.

Shear Zone. A narrow zoneof high deformation separating two blocks of crust.

Shield Volcano. A volcano built from low-viscosity mafic lava flows having very low relief.

Siderophile. A chemical element which has a strong affinity for molten iron and so will have tended to be concentrated in the Earth's core.

Silica. Silicon dioxide, SiO2. The most important single component of magma, making up between 45% to 90% of the composition by weight. Magma high in silica is extremely viscous, with the viscosity decreasing as the silica fraction decreases.

Silica-oversaturated. Describes an igneous rock that has an excess of silica beyond that needed to form feldspar, so that quartz is present.

Silica-saturated. Describes an igneous rock that has just enough silica to form feldspar, with little or no quartz or feldspathoid present.

Silica-undersaturated. Describes an igneous rock that is so low in silica that feldspathoids are present.

Sill. A horizontal intrusive body, lying between beds of the country rock.

Siltstone. A sedimentary rock formed mostly of clasts between 0.0625 mm and 2 microns in size.

Slab Pull. The force exerted by the weight of subducting crust at destructive margins, thought by some geologists to be the driving force for plate tectonics.

Slope-Forming Unit. A rock unit composed of relatively soft sedimentary rock, such as mudstones, shales, or poorly cemented conglomerates or sandstones, that erodes to a relatively gentle slope compared with more resistant beds above and below.

Sole Mark. Any distinctive marking left on the surface of a sediment bed by running water.

Solid Solution Series. A mineral in which one chemical element freely substitutes for another chemical element, so that the mineral has a range of compositions. For example, plagioclase feldspar forms a solid solution series ranging from pure albite (NaAlSi3O8) to pure anorthite (CaAl2Si2O8). Any number of calcium atoms can substitute for sodium atoms in the structure, so long as a matching aluminum atom simultaneously substitutes for a silicon atom.

Solidus. The temperature at which a mixture of minerals first begins to melt. Below the solidus temperature, the mineral mixture is completely solid; at or above the solidus temperature, the mixture is at least partially melted.

Sorting. Describes whether the clasts in a sedimentary rock (apart from matrix in the poor space) are all close to the same size. A well-sorted sandstone consists of clasts of uniform size. A poorly-sorted sandstone contains clasts varying considerably in size.

Splay. One of several branches off the end of a fault which help spread the displacement over a larger area.

Spreading Center. A location such as a mid-ocean ridge where two lithosphere plates are separating and rising mantle rock melts to produce new crust in the zone of separation.

Stagnation. Describes the process of magma from deeper in the earth pooling at that depth in the crust where its density matches the density of the country rock.

Stitching Pluton. A pluton injected into a suture that helps join the two blocks of crust together.

Stomata. Openings in the surface of land plants that control water loss. These were an essential evolutionary innovation for the conquest of dry land by life.

Stratovolcano. A volcano characterized by repeated eruptions of intermediate-silica ash and lava from a single vent over a long period of time that gradually builds up a high, symmetric cone. This is the type of volcano that most closely resembles the popular image of a volcano.

Strand. A branch of a fault that rejoins the main fault further along.

Stratigraphy. The branch of geology concerned with dividing rock beds into groups, formations, and members in order of age.

Streak. The color of a mineral when finely powdered. Produced by rubbing a sample on an unglazed porcelain plate. An important diagnostic property for some non-silicate minerals, such as hematite (blood-red streak).

Striation. A characteristic of certain minerals, of which plagioclase is the most common example, in which the surface is marked by very fine parallel grooves.

Strike-slip fault. A fault where the displacement is mostly in the horizontal direction.

Stromatolite. A stony structure, typically around a meter in height and diameter, built up by a microbial mat dominated by cyanobacteria.

Subalkaline. Describes igneous rock in which the alkali metal content is low enough that it is all incorporated into feldspars.

Subduction. The process whereby a tectonic plate is forced beneath another when the two collide.

Supereruption. A volcanic eruption of sufficient magnitude to devastate the entire region around the volcano and alter global climate. There is a scale for supereruptions called the Volcanic Explosivity Index, which uses terms like "mega-colossal" to describe points on the scale, suggesting somebody had too much time on his hands. The Valles caldera eruptions would likely rate as "mega-colossal" on this scale.

Supracrustal. Describes rocks deposited on an existing basement.

Suture. A zone of metamorphic and intrusive igneous rock that marks where two ancient plates collided and fused together. The Jemez Lineament is thought to be a suture between two Precambrian plates.

Tektosilicate. A silicate mineral in which silicon atoms are joined to each other by oxygen atoms to form a three-dimensional network. Quartz is an example of a tektosilicate. Feldspar is a tectosilicate in which some of the silicon atoms are replaced by aluminum atoms, with calcium, sodium, or potassium added to the crystal to supply the necessary electrons to allow aluminum to act like silicon.

Telosomes. Structures at the end of chromosomes that prevent them from unravelling.

Tephra. Fragments of rock produced by volcanic activity, such as ash, lapilli, or blocks.

Theia. A Mars-sized planetesimal thought to have impacted the Earth 30 million years after the formation of the Solar System, giving the Earth a large iron core and producing orbiting debris that coalesced into the Moon.

Therapsids. Tetrapod vertebrates that are the direct ancestors of the mammals.

Tholeiitic. Describes a suite of igneous rock formed in a reduced environment, so that olivine rather than magnetite crystallizes out early in its differentiation.

Thrust fault. A reverse fault with a shallow dip.

Tonalite. An intrusive igneous rock composed of plagioclase feldspar and at least 20% quartz, with less than 10% alkali feldspar.

Transcription. The process of producting protein molecules from DNA blueprints in living organisms.

Transgression. An advance of an ocean across a continent over geological time scales.

Trench Rollback. The process in which the point of subduction of a subducting plate migrates in the direction of the subducting plate. This often stretches the overriding plate to produce a back-arc basin.

Trondhjemite. A form of tonalite in which the plagioclase is particularly high in sodium.

Tuff. Any rock containing substantial volcanic ash. A welded tuff is deposited by a pyroclastic flow that is hot enough that the clasts are partially molten and weld together, while an unwelded tuff is deposited by a cooler flow in which the clasts are fully solidified. Volcanic rock eroded and reworked in a river environment can also be described as tuff.

Type Section. A geographical location where a formation was first carefully measured and described in order to assign it a formal formation name. If there is considerable variability within a formation, a type locality may be defined instead.

Ultramafic. Describes the most silica-poor igneous rocks, containing less than 45% silica. These are rare in the Jemez area.

Uncomformity. A gap in the sedimentary rock record where older beds are in contact with younger beds with a significant age difference across the gap.

Undepleted. Describes upper mantle rock that has had relatively little magma extracted from it, so that it still contains small amounts of alkaline metal oxides.

Underplating. A geological process in which dense magma from the upper mantle rises to the base of the crust but can go no further.

Unit Cell. The smallest piece of a crystal that contains the basis for its entire structure. A unit cell is always a parallelepiped, that is, a six-sided box whose sides are always parallel to the opposite side but need not necessarily be perpendicular to the adjoining sides.

Volcanic arc. A line of volcanoes that forms above a subducting oceanic plate. When the line of volcanoes erupts through shallow water, the volcanic arc may take the form of an island arc.

Volcaniclastic. A clastic rock composed of igneous clasts that have been transported a short distance from the eruptive center in which they formed.

Volcano. A mountain built up by repeated eruptions of around a single vent or cluster of vents.

Wacke. A sandstone containing more than 15% clay minerals in its pore spaces.

Xenolith. A patch of rock within an igneous bed that is different in composition from the rest of the bed. Xenoliths typically are chunks of country rock that were entrained in the magma and did not fully melt.

Zeolitized. Describes a sedimentary rock in which hydrous aluminum silicate minerals, known as zeolites, have been deposited to cement the clasts together. This typically occurs at the top of the water table in volcanic sediments.

Zircon. A mineral with the composition ZrSiO4 that is unusually resistant to weathering. Zircons also contain traces of uranium, and the decay of the uranium to lead can be precisely measured to determine the age of the grain. The oldest known substance on Earth is individual zircon grains that formed over 4 billion years ago.


This bibliography is not exhaustive. However, I've found these books and papers particularly useful.


Carmichael, Ian S.E; Turner, Francis J.; and Verhoogen, John. 1974. Igneous Petrology. McGraw-Hill, Inc. ISBN 0-07-009987-1

A somewhat dated but still very thorough and useful text on the basics of igneous petrology.

Fillmore, Robert. 2011. Geological Evolution of the Colorado Plateau of Eastern Utah And Western Colorado. Salt Lake City: University of Utah Press. ISBN 978-1-60781-004-9

Hands down the best discussion of the topic in print.

Kelley, Vincent C., and Northrop, Stuart A. 1975. Geology of Sandia Mountains and Vicinity, New Mexico. Memoir 29, New Mexico Bureau of Mines and Mineral Resources.

Describes the geology of the Sandia Mountains, which border the Jemez region to the south. Includes some interesting history of early geologic work in  New Mexico.

Klein, Cornelis, and Hurlbut, Cornelius S., Jr. 1993. Manual of Mineralogy (21st edition). John Wiley & Sons. ISBN 0-471-57452-X

Early versions of this standard reference go back over a century.

Kues, Barry S., Lewis, Claudia J. and Lueth, Virgil W. 2014. A Brief History of Geological Studies in New Mexico. New Mexico Geological Society Special Publication 12. ISBN 978-1-58546-011-3

A good review of the history of geological exploration and research in New Mexico.

Kutsche, Paul, and Van Ness, John R. 1981. Cañones: Values, Crisis and Survival in a Northern New Mexico Village.

An anthropological study of a small northern New Mexico village. Gives valuable insight into the traditional Hispanic culture in the area.

Levin, Harold L. 2010. The Earth Through Time (9th edition). John Wiley & Sons, Inc. ISBN 978-0-470-387740

Probably the best introduction to historical geology.

Lille, Robert J. 2005. Parks and Plates: The Geology of Our National Parks, Monuments, and Seashores. W.W. Norton and Company

Perhaps the best introduction to plate tectonics I've read. My only complaint, and it is a parochial one, is that the Jemez receive very little attention, due to Valles Caldera National Preserve not being part of the National Park Service at the time of publication.

Mack, Greg H., and Giles, Katherine A. (editors). 2004. The Geology of New Mexico: A Geologic History. New Mexico Geological Society Special Publication 11.

If you are familiar with basic geology, it's hard to recommend a better book for getting an overview of the geological history of New Mexico. The book has the readability one hopes for in a good review, with just enough technical details to please an expert without bogging down a dilettante.

McGhee, George R. Jr. 2018 Carboniferous Giants and Mass Extinction: The Late Paleozoic Ice Age World. New York: Columbia University Press. ISBN 978-0-23-118097-9

A dense but interesting discussion of life in the late Paleozoic and the sequence of mass extinctions culminating in the Permian-Triassic mass extinction.

Nédelec, Anne, and Bouchez, Jean-Luc (tr. Peter Bowden). 2015. Granites: Petrology, Structure, Geological Setting, and Metallogeny. Oxford University Press. ISBN 978-0-19-870561-1.

An excellent if somewhat technical discussion of intrusive rocks.

Philpotts, Anthony R., and Ague, Jay. 2009. Principles of Igneous and Metamorphic Petrology (2nd edition). Cambridge University Press. ISBN 978-0521880060

Probably the definitive textbook on the subject.

Rollinson, Hugh. 2007. Early Earth Systems: A Geochemical Approach. Blackwell Publishing

A good if somewhat technical introduction to the Hadean and Archean eons. Discusses the many questions that have still not been settled and the various answers that have been proposed.

Schmincke, Hans-Ulrich. 2004. Volcanism. Springer-Verlag. ISBN 978-3-540-43650-8.

An excellent and not too technical summary of the current understanding of volcanoes. Assumes a good understanding of basic geological concepts.


Kelly, Shari. Accessed 15 October 2016, "Tsiping".

Discusses the Tsiping ruins south of Canones.

Nava, Margaret. March 2008. "Exploring Gilman Canyon."  The Sandoval Signpost.

An interesting history of the Gilman Tunnels. 6 November 2013. "X-rays reveal inner structure of the Earth's ancient magma ocean."

Discusses the early magma ocean phase of the Hadean and the time scales for magma solidification.

Wall, Mike. 25 September 2013. "Was Ancient Earth Like Jupiter's Super-Volcanic Moon Io?"

Discusses a theory that the Earth at the end of the Hadean dissipated heat primarily through "heat pipes" rather than hot spots.

Shackley, M. Steven. 2015. "Sources of Archaeological Obsidian in the Greater Southwest."

Discusses the geological origins of obsidian found in archaeological sites.


Baars, D.L. 1974. "Permian rocks of north-central New Mexico" . New Mexico Geological Society Annual Fall Field Conference Guidebook Series. p. 167-169. Retrieved 5 June 2019.

A nice summary of the Permian formations of the Jemez region. 

Bailey, R.A., Smith, R.L., and Ross, C.S. 1969. "Stratigraphic Nomenclature of Volcanic Rocks in the Jemez Mountains, New Mexico". Geological Survey Bulletin 1274-P.

The classical paper on the stratigraphy of the Jemez volcanic field. Has aged remarkably well.

Ewing, Thomas E. 2019. "Proterozoic and Pre-Cenozoic History of the Sierra Grande Uplift and its margins: A Key Piece of the Ancestral Rocky Mountains". In Geology of the Raton-Clayton Area, Ramos, Frank; Zimmerer, Matthew J.; Zeigler, Kate; Ulmer-Scholle, Dana, New Mexico Geological Society 70th Annual Fall Field Conference Guidebook, 168 p.

Some interesting information on the Ancestral Rocky Mountains east of the Jemez area.

Galusha, Ted, and Blick, John C. 1971. "Stratigraphy of the Santa Fe Group." Bulletin of the American Musem of Natural History 144:1.

An older paper, but still valuable for its detailed discussion of the Santa Fe Group beds in the Espanola Basin.

Krainer, Karl, and Lucas, Spencer G. 2005 "Lithofacies of the Pennsylvanian Osha Canyon Formation at the type section, Jemez Mountains, New Mexico"  New Mexico Geological Society 56th Annual Field Conference. pp. 135-144.

The best recent paper on the Osha Canyon Formation.

Lucas, Spencer G; Krainer, Karl; Chaney, Dan S.; Dimichele, William A.; Voigt, Sebastian; Berman, David S.; and Henrici, Amy C. 2013. "The Lower Permian Abo Formation in Central New Mexico."  Carboniferous-Permian Transition in Central New Mexico. New Mexico Museum of Natural History and Science, Bulletin 59.

The best recent paper on the Abo Formation.

McLemore, Virginia T, Hoffman, Gretchen. 2005. "Mineral Deposits in Rio Arriba County, New Mexico". New Mexico Geological Society, 56th Field Conference.

A good and reasonable up-to-date summary of valuable mineral deposits in Rio Arriba County, which covers the northern Jemez area.

Premo, Wayne, and Kellogg, Karl. 2005. "Timing and Origin of Proterozoic Basement Rocks in the Sierra Nacimiento Region, NW New Mexico: Evidence From SHRIMP U-Pb Zircon Geochronology and Nd Isotopic Tracer Studies". Geological Society of America 2005 Conference.

The best recent paper on radioisotope ages of the Precambrian rocks of the Sierra Nacimiento.

Waresback, Damon B., and Turbeville, B.N. 1990 "Evolution of a Plio-Pleistocene volcanogenic-alluvial fan: The Puye Formation, Jemez Mountains, New Mexico." Geological Society of American Bulletin 102:3

A good description of the Puye Formation.

Whitmeyer, Steven J., and Karlstrom, Karl E. 2007 "Tectonic model for the Proterozoic growth of North America." Geosphere 3:4, pp. 220-259

The best summary of the Precambrian assembly of North America I've read.

Woodward, Lee A., Martinez, Ruben, DuChene, Harvey R., Schumacher, Otto L., and Reed, Richard K. 1974 "Precambrian Rocks of the Southern Sierra Nacimiento New Mexico" New Mexico Geological Society Guidebook, 25th Field Conference.

Rather dated, but describes the Precambrian rocks of the southern Sierra Nacimiento in some detail, with a simple map.

Woodward, Lee A., McLelland, Douglas, and Husler, J.W. 1977. "Precambrian Rocks of the Northern Part of the Nacimiento Uplift, New Mexico" New Mexico Geological Society Guidebook, 28th Field Conference.

Rather dated, but describes the Precambrian rocks of the northern Sierra Nacimiento in some detail, with a simple map.

Conference Proceedings and Other Reports

The NMGS conference proceedings are genuine treasures, combining numerous geological papers with at least three day's worth of road logs. However, the papers are aimed at professional or serious amateur geologists.

Baldridge, W. Scott; Dickerson, Patricia Wood; Riecker, Robert E. and Zidek, Jiri (ed.) October 1984. "Rio Grande Rift: Northern New Mexico" New Mexico Geological Society 35th Annual Field Conference

Road logs for Picuris Range; Amalia; and the Rio Grande Gorge and Ojo Caliente.

Bauer, Paul W., Kues, Barry S., Dumbar, Nelia W., Karlstrom, Karl E, and Harrison Bruce (ed.) September 1995. "Geology of the Santa Fe Region, New Mexico" New Mexico Geological Society 46th Annual Field Conference

Road logs for Santa Fe to Ghost Ranch via Cundiyo; Santa Fe to Pecos and Mineral Hill; and the Cerrillos His and Ortiz Mountains.

Goff, Fraser; Kues, Barry S, Rogers, Margaret Anne, McFadden, Les D, and Gardner, Jamie N.. (ed.) September 1996. "The Jemez Mountains Region" New Mexico Geological Society 47th Annual Field Conference

Road logs from Bernalillo to Los Alamos, from Los Alamos through the Valles caldera, and from Los Alamos through the Dome Road to Cochiti. Though slightly out of date, this is one of the finest of the conference reports, with some of the best road logs.

Koning, Daniel J., Karlstrom, Karl E., Kelley, Shari A., and Lueth, Virgil W. (ed) September 2011. "Geology of the Tusas Mountains and Ojo Caliente." New Mexico Geological Society 62nd Annual Field Conference

Road logs for the Ojo Caliente and Tusas Mountains, including many hiking trip options.

Kues, Barry S., Kelley, Shari A., and Lueth, Virgil W. (ed.) September 2007. "Geology of the Jemez Region II." New Mexico Geological Society 58th Annual Field Conference

Road logs for Los Alamos to Youngsville and back via the north caldera rim; Los Alamos to the Valles caldera moat; and Los Alamos to Ponderosa.

Open-File Geologic Map Series

These are another treasure, covering most of the area around the Jemez in detail. Most of the maps are accompanied by a detailed report describing the tectonic setting, formations, and structural features (such as fault zones) in the mapped area.

National Geologic Map Database

A few quadrangles of the Jemez area, particularly in the westernmost Jemez, are not yet part of the Open-File site. These can often be found in the National Geologic Map Database, although you first need to know the quadrangle name (which can be obtained from the Open-File site index map.)


Hayden, F.V. 1869. United States Geological Survey of Colorado and New Mexico.

The report of the Hayden Survey of the Front Range from Denver to Santa Fe. Hayden was a careful and skilled observer and the report makes excellent reading.

Herrick, C.L. 1900. "Report of a Geological Reconnoissance [sic] in western Soccorro and Valencia Counties, New Mexico." American Geologist 25:6

An interesting report on field work during the transition from classical geological surveys to modern detailed studies. C.L.Herrick was an early president of the University of New Mexico.

Wheeler, George M. and others. 1875-1889. Report upon United States geographical surveys west of the one hundredth meridian.

The report of the Wheeler surveys. Not nearly as readable as the Hayden report, with much bureaucratese; but includes the first good (for their day) maps of the Jemez region.

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