Aboriginesthe inhabitants who lived in the Big Bend before the time of the first European explorers.
Adobe brickthe name applied to a sun-dried brick. The bricks are made from adobe, a clayey deposit found in the desert basins of southwestern United States and Mexico.
Agatized woodthe replacement of wood by agate (silica) in such a manner that the original grain, form, and structure of the wood are preserved. The agate is a variegated waxy quartz (silica) in which the colors are in hands or in distinctive color patterns.
Alamothe Spanish name for a cottonwood tree. The term is commonly applied to streams, springs, and sometimes towns in the Southwest where there is a growth of cottonwood trees.
Algal reefa reef composed largely of algal remains in which the algae were the principal lime-secreting organism.
Ammoniteone of the large extinct groups of mollusks related to the living chambered nautilus. The divisions between chambers (sutures) are complex and angular as compared with the simple sutures in the nautilus. See Nautilus.
Angle of reposethe maximum slope or angle at which a material such as soil or loose rock deposit remains stable. When the angle of repose is exceeded, mass movement by slipping down the slope may be expected.
Anticlinea Structure characterized by arched strata and formed by folding of layered rocks. The two sides of the fold are inclined (dip) away from each other along a common ridge or axis, similar to the two opposite slopes in the roof of a quonset hut. Opposite of syncline, which is a downfold in the bedded rocks.
Anticlinal ridgea ridge formed by the arched beds in an anticline. Erosion may modify the folded ridge but commonly the crest of the anticline corresponds closely to the highest part of the ridge.
Arroyothe channel of an intermittent stream, normally with nearly vertical banks of unconsolidated rock material 2 or more feet high, and a flat-floored channel often covered with rock debris. The term arroyo is sometimes applied to all intermittent drainage channels found in the Southwest.
Ash (volcanic)See Volcanic ash.
Asymmetric folda fold in which the beds in one limb dip more steeply than in the other. If one limb becomes overturned, the term "overturned fold" is also used. See Overturned fold.
Badlandsa region nearly devoid of vegetation where erosion has cut the land surface into an intricate maze of narrow gullies (arroyos), sharp-crested ridges, and pinnacles. Traveling across such a region is difficult or almost impossible, hence the name badlands.
Badland topographya region in which badland features form the dominant land surface.
Bailethe Spanish word for a dance.
Basaltfine-grained, dark-colored igneous rock. It may be either intrusive or extrusive. Basalt is a common kind of lava. See Intrusion and Extrusion.
Basin (topographic)generally any depression on the earth's surface into which all the adjacent land drains, whether occupied by water or not, is termed a basin; an area having no outlet is a closed basin.
Bedthe smallest division of a stratified rock sequence, marked both above and below by a more or less distinct plane that separates one individual bed from the adjacent rock layers (beds).
Bedded formationa formation containing successive beds, layers, or strata.
Bedrocksolid rock, whether stratified or not, which underlies unconsolidated surface soil, sand, gravel, or clay.
Bedrock mortara depression in bedrock made by the Indians by grinding and used by them for hammering, crushing, and grinding grain. The procedure was similar to that used by early druggists who used a mortar and pestle for grinding drugs.
Bonitothe Spanish word for pretty.
Box canyona canyon having steep rock sides and a steep end, and normally a zigzag course.
Carranzathe President of Mexico during 1916.
Chiclethe Spanish word for chewing gum.
Cinco de MayoMay 5, the date (in 1862) that Mexico defeated Maximilian's army. One of the two important Mexican holidays; it is celebrated as is July 4 in the United States.
Cinnabarthe principal ore of mercury (HgS). Often called quicksilver.
Comanche moonSee Indian summer.
Conglomeraterounded water-worn rock fragments, cemented together by another mineral substance, similar in appearance to concrete. Sometimes called pudding stone.
Consequent streama stream whose course was controlled by the original slope of the land.
Contactthe place or surface where two different kinds of rock come together.
Continental depositsedimentary deposits laid down upon the land surface as contrasted with those laid down in the sea. They may be deposited in lakes, along Streams, or by the wind on dry land surfaces where there are neither lakes nor streams.
Continental shelfthe name applied to the shallow and gradual sloping ocean floor from the shore line out to a depth of about the 100-fathom (600 feet) line, beyond which the descent to the abyssal depths is abrupt. Most of the marine sediments (sandstone, shale, and limestone) are deposited on the continental shelf.
Continental slopethat part of the ocean floor extending from a depth of about 100 fathoms (600 feet) to about the 2,000-fathom depth (12,000 feet).
Correlationthe process by which stratigraphers attempt to determine the mutual time and rock relations of local sections.
Creepthe slow movement of finely broken rock materials or soils from higher to lower levels.
Cross-beddinginclined beds or laminations between the main bedding planes; the inclined beds are oblique to the main planes of stratification. False bedding.
Cross sectiona profile portraying a vertical section of the earth's crust.
Cuestaa Spanish word that generally applies to an unsymmetrical ridge with one slope long and gentle, generally agreeing with the top surface of the resistant bed that forms it, and the other slope steep or even precipitous, formed on the cut edges of the bed or beds that form the gentle slope.
Cut-and-fill featuresa feature resulting from the removal of one or more beds before the deposition of the overlying bed. Such features are often developed along stream meanders when there is cutting (erosion) on one side and fill (deposition) on the other.
Devils River Limestonea formational term applied during the early twentieth century to most of the massive Lower Cretaceous limestone units in the Big Bend. In this report, the Devils River Limestone has been subdivided into the Glen Rose, Telephone Canyon, Del Carmen, Sue Peaks, and Santa Elena Formations (see pp. 15, 118 and table 1).
Dikea tabular body of intrusive igneous rock that cuts the bedding of the host rocks.
Dike swarma set of generally parallel or radiating dikes.
Dinosaura class of extinct reptiles that lived during the Mesozoic Era. The term is rooted from the Greek words "dino" meaning terrible and "saur" meaning lizard; Terrible Lizard.
Dipping bed, dipthe angle at which any bed, stratum, or planar feature is inclined from the horizontal.
Displacementsee Fault displacement. Displacement may also be caused by igneous intrusions, folding, and slump (landslides).
Domea roughly symmetrical upfold in the rock layers; the beds dip more or less equally in all directions from a central point. A homely example would be to place a round vegetable bowl upside down on the table and spread the table cloth evenly over the bowl; the upward bulge in the table cloth would represent the dome. Opposite of a basin.
Dome crestthe top of the upfold (dome); highest point on the dome.
Dome mountaina mountain resulting from domical upfold in the bedded rocks. Its form and the lack of plications in the exposed rocks suggest that the originating force pushed upward from beneath rather than laterally. This type of mountain is common in the western United States.
Downdropped or downthrown sidesee Fault, downthrown side.
Ensilagechopped forage (fodder) stored in a silo and used for feeding livestock.
Epocha subdivision of the periods in the geologic time scale. Example, Eocene. See geologic time scale, figure 5.
Eraa large division of geologic time including several periods. See geologic time scale, figure 5.
Erosionthe wearing away and removal of the rocks or soils of the earth's crust.
Eruptionin geology, the emergence of molten rock from a vent at the earth's surface.
Escarpment or scarpthe steep face of a ridge or mountain range. The escarpment normally abruptly separates the mountain range from adjacent level or gently sloping areas.
Escopetathe Spanish word for shotgun.
Estufa (canyon)the Spanish word for stove (generally cookstove); Estufa (stove) Canyon.
Extrusionthe act or process of thrusting or pushing out. In geology the term is normally applied to the emission of lava or other volcanic material at the earth's surface.
Extrusive rocksa term applied to those igneous rocks derived from magma (molten rock beneath the surface) or magnetic materials that poured out or were ejected at the earth's surface; as distinct from the intrusive igneous rocks that cooled and solidified from magmas that invaded older rocks at depths.
Familya taxonomic division used in the classification of animals and plants.
Faulta fracture or fracture zone in the rocks along which there has been relative displacement of the two sides parallel to the fracture. The displacement may be a few inches, hundreds of feet, or many miles. See Fault displacement.
Fault blocka rock mass bounded on at least two sides by faults.
Fault block mountaina fault block raised to form a mountain. Such mountains are normally carved by later erosion and are hounded by an escarpment on at least one side.
Fault displacementdisplacement or dislocation is the relative movement of rocks on opposite sides of a fault. The movement may be vertical, horizontal, or both, and the displacement is measured as the distance between the broken ends of the same bed or formation as measured along the fault.
Fault, downthrown or downdropped sidethe block of rock that has moved downward along the fault relative to the other side See Relative movement.
Fault escarpment (scarp)an escarpment that coincides more or less closely with a fault. The escarpment normally occurs on the high side of the dislocation in the Big Bend National Park. See Fault-line scarp.
Fault-line scarp (escarpment)a scarp (escarpment) which has been produced by differential erosion along a fault line. Erosion normally causes the escarpment to recede so that the fault-line scarp may be hundreds of feet or even miles from the true fault line.
Fault, normalsee Normal fault.
Fault scarpthe cliff formed by a fault. Most fault scarps have been modified by erosion since the faulting.
Fault, thrustsee Thrust fault.
Fault tracethe intersection of a fault and the earth's surface.
Fault trougha relatively depressed fault block lying between Iwo faults with roughly parallel trace. See Graben and Rift valley.
Fault, sapthrown sidethe block or mass of rock on the side of a fault that has been displaced relatively upward. The term refers to the relative movement and not an absolute displacement. Opposite of downthrown side.
Faunathe animals (collectively) of any given formation, age, or region.
Fetlockpart of horse's leg where a tuft of hair grows behind the pastern joint.
Fiestathe Spanish word for a holiday or celebration.
Fissurea crack, break, or fracture in the rocks. Fissures normally have well-defined boundaries that constitute the sides; some of them have been filled with minerals, but many of them are open passages.
Flaggystrata from 10 to 100 mm (about 0.4 to 4.0 inches) thick which have a platy or tabular character.
Flagstonea rock that splits readily into slabs suitable for flagging.
Flood plainall great rivers annually flood portions of the level land along their banks, especially near their mouths, and cover them with sedimentary deposits. The area thus flooded is called the flood plain. Generally called bottom land in western United States.
Florathe plants (collectively) of a given formation, age, or region.
Folda bend in the strata (bedded rocks). The upfolds (arches) are called anticlines the downfolds synclines.
Fold axisthe line following the apex of an anticline or the lowest part of a syncline.
Foot wallthe mass of rocks beneath the fault plane.
Formationthe fundamental unit in rock stratigraphic classification. A formation is a body of rock characterized by lithologic homogeneity; it is prevailingly but not necessarily tabular and is mappable at the earth's surface or traceable in the subsurface.
Fossilthe remains or traces of animals or plants which have been preserved by natural causes in the rocks of the earth's crust.
Foxfirethe phosphorescent light emitted by rotting wood.
Fracturea break in the rocks.
Fresh-water depositsediments deposited in a lake or other water body that does not contain the mineral salts normally found in sea water.
Fresnothe Spanish word for ash tree.
Frijolesthe Spanish word for pinto or speckled brown beans.
Frost actionthe action of freeze (expansion) and thaw which is a powerful weathering agent and eventually causes disintegration of rocks.
Glacial climatethe cold climate normally associated with periods of glaciation.
Glaciera mass of ice having definite lateral limits and motion in a definite direction that has originated from the compaction of snow in the snowfield that feeds the glacier.
Glass (volcanic glass)natural glass produced by the rapid cooling of molten lava. The rate of cooling is too rapid to permit crystallization, which results in the formation of obsidian and pitchstone.
Glochidsa cluster of tiny spines on the pads of the prickly (blind) pear.
Grabena block of the earth's crust, generally long as compared to its width, that has sunk between two or more faults. The surface of the depressed block is normally low as related to the surface on the opposite sides of the bounding faults.
Grainsin geology, the particles or discrete crystals which comprise an igneous rock; the individual particles that comprise a sedimentary rock, as the sand grains in a sandstone.
Grain sizea term relating to the size of mineral particles that make up a rock whether igneous or sedimentary. Such terms are normally expressed as fine-, medium-, or coarse-grained.
Granitea coarse-grained, light-colored, igneous rock composed of pink or gray feldspar, quartz, and commonly mica or hornblende.
Granulara textural term applied to igneous rocks in which the mineral grains are more or less granular, and to sedimentary rocks made up of granular grains.
Gravelan unconsolidated accumulation of pebbles mixed with sand grains and granules. The word gravel is generally applied when the size of most of the largest pebbles does not exceed that of an ordinary hen's egg. If the gravel is cemented with mineral matter, it is normally called a conglomerate.
Grindingthe wearing away of rock materials through the effect of continual contact, pressure, and abrasion by other rock particles.
Gully erosionthe removal of soil, weak rock materials, sand, etc., by running water during heavy rainfall. On farms, the term is often applied to any erosion channel that cannot be eliminated by plowing.
Habitatthe environment in which the life needs of a plant or animal are supplied.
Hanging wallthe mass of rock above the fault plane.
Herbiverousanimals that feed on herbs or other vegetable matter. Opposite of carniverous (flesh eaters).
Heterogeneousas applied to rocks, commonly conglomerates, the pebbles show great variation as to size, kind, composition, color, hardness. Antonym, homogeneous.
Hillhill and mountain are relative terms with respect to each otherthe highest elevations are designated mountains and the lower elevations, hills. Some would class all elevations of 1,000 feet or more as mountains and the gradational features between the higher and lower features as foothills. Normally, the term hill is used to designate a mass that rises conspicuously above the level of the surrounding country, regardless of the elevation, and culminates in a well-marked crest or summit.
Hogbacka term commonly applied to a sharp-crested ridge formed by a hard rock ledge that dips steeply beneath the earth's surface. Due to resistance to erosion the hard rock ledge rises boldly above the weaker rocks that surround it. See Cuesta.
Hornfelsa fine-grained, tough, hard, non-laminated metamorphic rock resulting from contact metamorphism (baking). See Metamorphism. Most hornfels in the Big Bend are black: they are conspicuously exposed on the west flank of the McKinney Hills.
Horsetrapa fenced enclosure with sufficient forage to sustain a few horses, The mounts used regularly on a ranch are kept in the horsetrap, where they can forage for themselves but are readily available.
Huacamolea green salad consisting chiefly of mashed avocado, with chopped onion, tomatoes, and seasoning spices.
Huarachesthe Spanish word for sandal. The early Mexican huaraches were made from untanned leather, not decorated, and were fastened to the feet by rawhide strings. In recent years, most of the locally made Mexican huaraches along the Rio Grande have been made from pieces of automobile tires.
Ice agethe glacial period.
Igneousrocks formed by solidification from a magma, or partially molten materials. One of the two great classes into which most rocks are divided. Contrasted with sedimentary rocks.
Igneous intrusionA body of igneous rocks that invaded older rocks and solidified beneath the earth's surface.
Imperviousterm applied to strata such as clay and shale which do not permit the penetration of water.
Indian summera period of warm, quiet, hazy weather that may occur in late September, October, or early November; in some years there may be only a few days or none at all, while in other years. there may be one or more extended periods. The Indian summer period includes the time of the Mexican or Comanche moon.
Indurated rockhard rock. In normal usage. the term applies to rocks hardened by cementation, by pressure, or by heat, or any combination of these agencies.
In situ, or in placein its natural position or place; in geology, said specifically of a rock, soil, or fossil found in the situation or place where it originally formed or was deposited.
Intermittent streama stream which flows but part of the time, as after a rainstorm or during but part of the year.
Intermontane basina basin lying between mountain ranges, common in the Great Basin region.
Intrusive or intrusive rocksin geology, a mobile mass that penetrates into or between other rocks and which has solidified beneath the earth's surface.
Invertebrate fossilfossil of an animal having no backbone or spinal column. See Vertebrate.
Jacalthe Spanish word for a small adobe, rock, or rock and adobe hut.
Jointin geology, a fracture or parting which interrupts abruptly the physical continuity of a rock mass.
Jointed rocksrocks that are fractured in a consistent pattern. See Joint.
Laccolitha concordant, intrusive body that has spread laterally between rock layers, doming the overlying rocks but not deforming the underlying rock; thus a laccolith normally has a horizontal or nearly flat base and is mushroom- or tackhead-shaped.
Lagoona pool or lake of shallow water, normally salty, near the seashore and often connected to the ocean by a narrow passage. The quiet water on the land side of a barrier island; example, Laguna Madre on the Texas Gulf Coast.
Land formthe term land form is applied by physiographers to each one of the multitudinous features that taken together make up the surface of the earth.
Land sculpturethe carving of physical features by natural causes, chiefly by running water but also by waves, wind, and glaciers.
Landslidethe downward sliding or falling of a relatively large mass of earth, rock, or mixture of both from a mountain or any steep slope to a lower level. Landslide action is commonly triggered by excessive rainfall.
Lavafluid rock such as that which issues from a volcano or a fissure to the earth's surface; also the same material solidified by cooling on the earth's surface.
Lava flow(1) a river or sheet of fluid, viscous, or partially solidified lava that issues from a volcanic vent or from a fissure in the earth's crust. (2) The solidified, stationary mass of rock formed when the lava congeals on the earth's surface.
Ledgea term commonly applied to one or several beds of hard rock occurring in a hill-side; a narrow shelf-like projection from the face of a steep declivity.
Lignitea brownish-black low-rank coal in which the alteration of the vegetable material has proceeded further than in peat but not so far as in subbituminous coal.
Limestonea bedded sedimentary deposit consisting chiefly of calcium carbonate (CaCo3). Limestones contain 50 percent or more of the carbonates of calcium or magnesium and are widely distributed on the earth's surface.
Lithologya term commonly used to refer to the composition of a rock.
Loadthe sediments moved by a stream, whether in suspension (floating) or being rolled and pushed along the stream's bottom.
MagmaNaturally occurring molten rock.
Mammala warm-blooded vertebrate animal that brings forth its young alive and suckles the young.
MarlA calcareous clay, or intimate mixture of clay and calcium carbonate, usually with fragments of shells. The term marl is also often applied to soft, impure limestone.
Massivein this report, the term massive is used to describe sedimentary strata that are 3 or more feet thick, normally hard, free of minor joints and laminations, and having homogeneous physical characteristics.
Meandering (stream)the characteristic habit of a stream that winds freely on a broad flood plain.
Member (of a formation)a division of a formation, generally of distinctive character, containing a specific fauna or of local extent.
Mesaa tableland; an elevated, flat-topped land form bounded on at least one side by a steep cliff. Mesa is a Southwestern term and is more often applied to small areas (several square miles) rather than to large features which are more properly called plateaus.
Metamorphic rocka rock that has been metamorphosed. See Metamorphism.
Metamorphisma change induced in a rock by high temperatures and pressures. For example, when a limestone is deeply buried in the earth's crust, the higher temperatures cause the calcite to recrystallize and a marble is formed. The limestone has been metamorphosed.
Metatethe Spanish word for a dish-shaped or hollowed-out stone used for grinding grain.
Mexican moonsee Indian summer.
Minerala naturally occurring, homogeneous inorganic substance, having crystalline structure and normally a definite chemical composition. Most minerals contain impurities.
Mineral depositan accumulation of minerals.
Mineral-springa spring whose waters contain mineral salts.
Morralethe Spanish word for a knapsack, nosebag for feeding horses, shopping bag, hunter's bag, etc.
Mortarin this report, a rock vessel in which the Indians ground or pounded grain with a rock pestle to make flour. See Metate.
Mud cracks (sun cracks, shrinkage cracks)a regular system of cracks formed when mud sediments lose water. The cracks form a polygonal pattern.
Muy malothe Spanish words for "very bad"; often applied to degree of sickness or to a person's general physical condition.
NautilusOne of the cephalopods having an externally chambered shell, coiled planispirally, with enlarging whorls in direction of living chamber. The divisions (sutures) between the chambers are straight or simply curved as contrasted with highly irregular sutures of its extinct relative, the ammonite.
Necksee Volcanic neck.
Normal faulta fault in which the hanging wall has dropped relative to the footwall.
Nuggeta water-worn piece of native gold.
Obsidiannatural volcanic glass. Most obsidian is black, although color may be red, green, or brown.
Ordera category in the classification of animals and plants, ranking between a family and a class; an order is composed of several families. See Family and Class.
Orea metalliferous mineral or aggregate of metalliferous minerals that can be mined and treated at a profit.
Organicpertaining to living things (animals and plants) or to those plants and animals that once possessed life.
Outcropthe exposure of rock at the earth's surface.
Overthrust faultfracture along which one mass of rock has overridden another wherein the hanging wall (relatively) has moved over the footwall.
Overturned folda fold in which the beds on one limb have been tilted past the vertical position so that they are inverted in the outcrop.
Paleontologythe science that deals with the study of both fossil plants and animals from past geologic ages.
Partinga small fracture in the rocks.
Passa gap, or other relatively low break, in a mountain range, or valley between ranges, through which a stream, road, or trail passes.
PeatA dark brown or black soft substance produced by the partial decomposition, disintegration. and carbonization of vegetation in bogs or marshes. The formation of peat is an early stage in the development of coal.
Periodthe fundamental unit of the standard geologic time scale. Example, Devonian Period. See geologic time scale, figure 5.
Pervious bed (rock)a bed or stratum with pores through which fluids can move.
Petrifyto become stone. Organic substances, such as shells, bones, and wood, embedded in sediments, become converted into stone by the gradual replacement of their tissue, particle by particle, by mineral matter. Commonly, not only the outward form but even the minutest details of the organic tissue are preserved.
Petrified wood (silicified wood)wood replaced by silica.
Petroleuma naturally occurring substance composed predominantly of carbon and hydrogen compounds. Petroleum may occur as a liquid, gas (natural gas), and/or in a solid (asphalt) state depending on the nature of these compounds and the existing conditions of temperature and pressure.
Physiographyphysiography has to do with description of land forms.
Plug or plug-like massan intrusive mass that cut through and deformed the older rocks.
Porositythe ratio of the aggregate volume of voids in a rock or soil to its total volume.
Porouscontaining voids, pores, interstices, or other openings which may or may not be connected.
Presidiothe Spanish name for fortress or prison and also a place where troops were garrisoned. In addition to the fortress, the early presidios also included a religions chapel.
Primitive fossilfossilized remains of the earliest simple life.
Producer's gasa combustible gas manufactured from coal.
Prospectthe name given to any mine workings, the value of which has not been determined.
Prospectingsearching for new mineral deposits; also, preliminary exploration to test the value of a mineral deposit already known to exist.
Relative movementin studying structural features, for example, faults, it is often impossible to determine which block actually moved, Thus, most displacements can be discussed only in terms of relative movement, that is, block A moved relative to block B. The downthrown side in a normal fault is the one that shows the relative downward movementboth sides may have moved down, but the downthrown side moved down farther in relation to the upthrown side.
Remudathe Spanish word for a group of horses. Also a term commonly applied to a herd of spare horses or spare pack animals.
Relief(1) The elevations or the inequalities (collectively) of a land surface, (2) The difference in elevation between the high and low points of a land surface.
Retorsely barbedbarbs bent or turned backward.
Rhizomesan underground bulbous stem that produces roots below and leaves and bloom stalk above. Example: iris.
Rhyolitethe extrusive equivalent of a granite. Rhyolites are normally fine grained or have visible crystals scattered through a fine groundmass; some rhyolites are glassy.
Rift valleyan elongate valley formed by a depressed block of the earth's crust that lies between two or more faults with approximately parallel trends. See Graben.
Rimrockrocks or rock ledge forming a natural and commonly precipitous boundary of an elevated land form.
Ripple-markan undulating surface produced in sand or non-coherent materials by the wind, by currents, or by wave action.
Roadrunnera long-tailed, slender, ground cuckoo that inhabits the open region of the Southwest. It spends most of the time on the ground and can run with great swiftness. It is commonly also called the chapparal [bird] and by the Latin-Americans, paisano (fellow countryman ).
Rockstrictly, any naturally formed aggregate or mass of mineral matter, whether or not coherent, which constitutes part of the earth's crust. Commonly, however, the term rock is applied only to firmly consolidated mineral masses, which would exclude loose unconsolidated sand or gravel and soft clay.
Rollthis term is variously used to describe minor deformations or dislocations. In this report it applies to small folds in thin-bedded weak rock that was folded when supporting strata were removed by solution and the overlying mass collapsed or slumped.
Runoffthe water which flows on the earth's surface.
Saddlea low point in the crestline of a ridge, often a divide between the heads of streams flowing in opposite directions.
Sandan unconsolidated detrital material consisting predominantly of quartz grains.
Sandstonea cemented or otherwise compact detrital sediment composed predominantly of quartz grains, the sizes of the grains being those of sand.
Sappingthe process of weathering and erosion that causes the disintegration and removal of weak rock layers underlying a more resistant bed; due to the lack of support, the upper resistant bed collapses and fragments tumble down the mountain slope.
Saturateda rock or soil is saturated with respect to water if all its interstices (voids) are filled with water.
Scarpan escarpment, cliff, or steep slope.
Schistmetamorphic rock with a foliated structure.
Sedimentary rocksrocks formed by the accumulation of sediments following deposition from a transporting medium such as water (aqueous deposits), air (eolian deposits), or both. The sediments consist of rock fragments of various sizes (conglomerate, sandstone, shale); the remains or products of animals or plants (certain limestones and coal); the products of chemical action or of evaporation (limestone, salt, and gypsum); or mixture of the above materials. Some sedimentary deposits (tuffs) are composed of volcanic ash and are deposited either on land or in water. A characteristic feature of sedimentary rocks is their layered structure, known as bedding or stratification. Each layer is a bed or stratum; the layers are deposited in a flat, or nearly flat, position. When sedimentary rocks are observed that are not in a nearly flat position, they have been deformed by forces that deformed the earth's crust. See Igneous rock for contrast of origin.
Seepa place where water oozes from the earth, often forming a spring.
Semiariddescriptive term for an area of low rainfall; a subdivision of climate in which the associated plants are spiny shrubs, stunted trees, and short grasses, whereas a subhumid climate is characterized by tall trees and grasses.
Shalea laminated sedimentary rock in which the constituent particles are predominantly clay (consolidated mud).
Sheet erosionerosion accomplished by sheets of unchanneled running water.
Sheetfloodunder certain conditions, essentially unchanneled sediment-laden water flows over an erodable surface in a sheet. This is termed sheetflood.
Shut-in or Shut-upa narrow gorge with steep sides in a broader valley.
Sierraa Spanish word for mountains. More strictly applied to mountain ranges that have a jagged crest.
Silla tabular intrusive body of igneous rock which conforms to the bedding or structure of the host rocks.
Slumpwhen the soil, rocks, or any earthy material on a slope becomes unstable and moves down the slope under the influence of gravity, it is said to have slumped.
Sortingas applied to sediments, the dynamic process by which material having the same peculiar characteristics, such as size, shape, or specific gravity, is separated from a larger heterogeneous mass.
Speciesa group of individuals (animals or plants) having substantially the same structure, habits, geographic and geologic range, which normally interbreed, producing like kind.
Sponge spiculea small, slender, spindle-shaped, sharp-pointed body that forms part of the skeleton or supporting framework of the sponge.
Stratificationthe planar structure in beds or layers of strata. A common characteristic of sedimentary rocks.
Structurestrictly, and properly, structure is the sum total of all the structural features (rock deformations) in an area. However, commonly, a particular feature, such as an anticline is referred to as a structure.
Symmetrical folda fold with an essentially vertical axial plane so that the two limbs are symmetrical.
Synclinea fold in rocks in which the strata dip inward from both sides; a downfold. The opposite of anticline.
Tanka small artificial depression in which water collects. It is used chiefly for watering livestock. The term is commonly used in the arid Southwest and is synonymous with the term pond in many areas.
Tequilaan alcoholic beverage made from the century plant (maguey).
Terracea relatively flat, horizontal or gently inclined surface, sometimes long and narrow, which is bounded by a steeper ascending slope on one side and a steeper descending slope on the opposite. Generally formed along stream courses.
Throwthe amount of vertical displacement along a fault.
Thrust faulta fault that is characterized by inclination of the fault plane where the hanging wall (upthrown side) has moved over the footwall (downthrown side), thus causing shortening in the earth's crust.
Tinajathe Spanish word for a natural bowl, bowl-shaped cavity, or hole in the bedrock in which water accumulates.
Tornillothe Spanish word for screw and applied to a species of scrubby tree in the Southwest that has a seed pod with coiled revolutions similar to those of a common wood screw.
Trans-Pecos Texasthat part of Texas that lies west of the Pecos River; the area bounded on the northeast and east by the Pecos River and on the southwest and south by the Rio Grande. Some persons consider southeastern New Mexico as a part of the Trans-Pecos region.
Truncategeologically applied to rock units and structure cut by an erosion surface.
Tuffconsolidated volcanic ash.
Tunathe Spanish word for the fruit of a prickly pear.
Unconformitya surface of erosion or non-deposition, especially the former, that separates younger rock layers (strata) from older rocks. Commonly, the stratification in the two sequences of rocks intersects at an angle and this relationship is normally designated as an angular unconformity.
Upthrowthe block or mass of rock on that side of a fault that has been displaced upward.
Vent (volcanic)an outlet, through which volcanic ejecta erupted on the earth's surface.
Vertebratean animal having a backbone or spinal column, such as in mammals, birds, and fishes.
Villaone of the Mexican revolutionists during 1910-18.
Viva Carranzahurrah for, or long live Carranza.
Viva Villahurrah for, or long live Villa.
Volcanic ashuncemented material consisting of fine rock fragments or volcanic glass, produced during the explosive action of volcanoes. If the ash is later cemented into a compact (indurated) rock mass, it is called tuff.
Volcanic conea cone-shaped eminence formed by volcanic discharge.
Volcanic cratera steep-walled depression on top of a volcanic cone, directly above the vent that feeds the volcano.
Volcanic neckthe solidified material filling the vent of a dead volcano.
Volcanic rocksthe igneous rocks that have been poured out at the earth's surface by volcanic activity. The term is synonymous with extrusive rocks.
Volcanoa vent in the earth's crust from which molten lava, ash, cinders, and gases issue; the mound of volcanic ejecta.
Weatheringaction by chemical and physical processes which attack rock at the earth's surface.
Windchargera small wind-powered electric generator. Those used in the Big Bend during the mid-1930's were commonly mounted on a tower up to 20 feet high and when the velocity of the wind was 15 to 20 miles per hour they would light two to three 50-watt bulbs. Naturally, there was some variation in the brightness of the lights unless the voltage was regulated by storage batteries. The windchargers were stocked by some of the larger trading posts and they could be obtained from some mail order houses for about $17.50 each.
Wind gapa low depression or notch in a mountain range where a stream formerly flowed. Wind gaps are places where mountain ranges are most easily crossed and as such were exploited by transportation routes, first by stages and wagons, then by highways and railroad.
Last Updated: 22-Jun-2009