The Western San Juan Mountains: Their Geology, Ecology, and Human History

Glossary

GLOSSARY This glossary includes some of the more commonly used terms in the text. It is not a complete listing ofall technical terms. For more in-depth definitions please consult technical dictionaries or general texts in geology, biology, and archaeology. ablation: processes by which snow and ice are lost from a glacier (wastage). adsorption: adhesion of gas molecules or gas molecules in solution to a solid surface by weak molecular bonding. algal mounds: small hill-shaped limestone structures formed by the remains of ca1cium-carbonate-producing algae. alluvial: associated with or formed by running water (e.g., streams or rivers). alpine: associated with high mountains (e.g., the Alps of Europe); more specifically, associated with areas above timberline. andesite: a dark-colored, fine-grained rock ofvolcanic origin containing sadie plagioclase feldspar and one or more ofthe mafic minerals (e.g., biotite, hornblende, pyroxene). angular unconformity: an erosion surface in which younger sediments rest upon tilted or folded older rocks. annual: a plant that completes its entire life cycle and dies within a single year. anticline: a fold, sides down and center up, wherein the core contains older rocks. arboreal/arborescent: associated with, or living in, or having the form of a tree. Archean: the earlier part ofPrecambrian time (see Stratigraphic Chart, p. 2). arete: a sharp-edged ridge or spur, commonly found above the snowline in rugged mountains, formed by glacial action in the heads ofvalleys and the backward growth of adjoining cirques. asexual reproduction: reproduction that does not involve sex (i.e., there is only one parent, and the offspring are genetically identical to the parent). 365 366 The Western San juan Mountains association: a group ofplant species that tend to occur together in places having similar environmental conditions. asthenosphere: the layer of the earth below the lithosphere; the soft, probably partially molten layer where magmas arc generated. basalt: a fine-grained, dark, mafic igncous rock composed largely of plagioclase feldspar and pyroxene. basement: the oldest rocks in a given area, a complex of igneous and metamorphic rocks that underlies all of the sedimentary formations. basin: 1. a depressed area with no surface outlet; 2. the drainage area of a stream; or 3. a low area in the earth's crust where sediments have accumulated. batholith: a large igneous body formed from the cooling of magmatic rock at depth with extensive surface exposure. biota: all ofthe various forms ofplants, animals, and microorganisms that live in an area. breccia: rock formed by angular broken fragments ofolder rocks held together by a mineral cement or a fine-grained matrix. caldera: a large, basin-shaped, generally circular volcanic depression commonly formed by collapse of the magma chamber beneath a volcano after venting. carbonaceous: rich in carbon or organic matter; perhaps containing coal. carbonate: 1. a mineral containing the anionic structure of C03-2 (e.g., calcite and aragonite CaC03); 2. a sediment formed ofthe carbonates of calcium, magnesium, and/or iron, e.g. limestone and dolomite. carnotite: a strongly radioactive, canary-yellow to greenish-yellow secondary mineral; an ore for uranium and vanadium. cirque: a steep-walled semicircular hollow, high in a mountain valley, formed by erosive glacial action. clastic: formed from mineral particles (clasts) that were mechanically transported. co-evolution: adaptation or other forms ofevolution that takes place in two closely associated species in response to the effects ofone on the other. Colorado lineament: a hypothesized belt ofPrecambrian faults or zones ofweakness in the basement about 100 miles wide, extending northeastward from the Grand Canyon to the Rocky Mountain ftont near the Colorado-Wyoming border. columnar jointing: the breaking ofan igneous rock into parallel, prismatic columns by cracks produced by thermal contraction upon cooling. community (biotic community): an assemblage of organisms of many different species that all live and interact with one another within a particular area. Glossary 367 cordillera: an extensive series of mountain ranges. creep: 1. the slow, imperceptible downslope movement of rock and soil caused by gravity; 2. slow deformation of solid rock resulting from constant stress over a long period of time. cuesta: a landform consisting of a ridge with one steep side and one gently sloping surface (often less than 5 degrees dip). debris flow: a moving mass of rock fragments, soil, and mud, more than half of the particles being larger than sand size. Rates vary from less than 1 meter per year to more than 150 kilometers per hour. desiccation: the process...