DESERT VARNISH - A dark, shiny coating on rock, caused by years of intense sunlight on the rock surface. This sample shows both varnished and unvarnished Entrada Sandstone. The varnished portion contains Anasazi petroglyphs.
ADOBE - A dark, clay-rich soil, characteristic of arid and semi-arid regions
AEOLIAN (see EOLIAN)
ARIDISOLS (Desert Soils) - In areas of low humidity, water tends to evaporate away, rather than running off. Thus, salts of various kinds tend to accumulate. In addition, there are lower amounts of organic matter, because the soil supports less life. Aridisols, or desert soils tend to be light on color, and contain higher concentrations of chlorides, sulfates, or carbonates. These salts can locally concentrate in the certain layers or horizons in the soils. Caliche (see below) is a typical carbonate layer in desert soils. Typically these soils are alkaline (non-acidic), but may be less so in areas where silica concentrates. Much depends on the source rock. The Basin-Range province, which is coincidentally mostly desert, has many carbonate-bearing formations in the central and southern areas. Soils in these areas tend to be carbonate-rich. To the west and north, this is modified by the presence of extensive volcanic complexes. and the resulting soils are more complex as well, containing more exotic minerals such as zeolites. All may be clay-rich. As expected, these soils are not the best growing environments, requiring large amounts of imported water to support growth. Such flooding can mobilize the soil salts, which further impacts agriculture uses, and long-term can render the soils infertile.
ALKALI - Concentration of base ions, such as hydroxyl or carbonate, in the soil (Alkali Soils), and as pure deposits in dry lake beds (Alkali Lake)
ALLUVIUM - Detrital material deposited by running water. Usually a mixture of clay, silt, sand, and gravel.
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BEDROCK - Consolidated, usually indurated rock, often exposed in arid climates, due to water and wind erosion. |
CALICHE - Crust of lime that forms in or on desert soils.
DESERT ROSE (or Barite Rose)
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DESERT VARNISH - A dark, shiny coating on rock, caused by years of intense sunlight on the rock surface. This sample shows both varnished and unvarnished Entrada Sandstone. The varnished portion contains Anasazi petroglyphs. |
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EOLIAN - Processes relating to the wind, and its effects on the rock and soil. A more prominent effect in desert regions.
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EROSIONAL REMNANT - A vestigial bedrock formation, remaining after extensive erosion. |
ESCARPMENT - A semi-linear rapid change in elevation, possibly cliff-like, and generally representing faulting in conjunction with erosional action.
FORMATION - A cohesive rock unit, usually some uniform sedimentary series, that can often be traced for hundreds of miles through the arid regions because of poor soil development.
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GRABEN - The low part of the structure formed as a result of parallel pairs of normal faults. See "Horst". |
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GROUP - A geologic term for a related collection of formations, either spacially (found together), or representing a succession of paleoenvironments.
HORST - The raised structure formed as a result of parallel pairs of normal faults, complementary to grabens. These two structures together are called "Horst and Graben Terrain", and accounts for much of the major topography seen in the Basin and Range Province.
LOESS - A group of soils, largely comprising silt or finer grains, of supposed wind-deposited (glacial) origins.
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OASIS - An isolated, fertile or otherwise green, water-rich locality in a desert region. |
OPAL (Common Opal, Precious Opal, Fire Opal.) Hydrous silicon dioxide. A common mineraloid in certain desert areas, requiring more arid conditions for its continued preservation. Not a true mineral, because of its variation in composition.
OPALIZED WOOD - Ancient wood that has been replaced by hydrolyzed silica, maintaining the original wood structure.
PLATEAU - An extensive raised, largely flat-lying area.
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SHORELINE - Erosional and/or depositional remnants of an ancient lacustrine boundary, (lakeshore). |
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STEPPE - Arid, usually fairly level land, marked by loess soils. Asia and Africa have enormous Steppe regions bordering their deserts.
STRATA - The individual layers in a sedimentary sequence.
TALUS - A steeply-sloping deposit of unconsolidated debris, adjacent to bedrock.
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Classic Tufa scene on the shores of Mono Lake. For more information on Mono Lake and its current condition, please visit this web site. |
TUFA - A mineral condensate which forms when two bodies of water meet that have different chemical composition, such as the spring waters that enter Mono Lake. These condensates can form large complex structures such as those seen in the above example. |
VENTIFACT - A rock that has been shaped and polished by the wind, with the help of blowing sand and silt particles.
WATER TABLE - Roughly equivalent to "Piezometric Surface" - the depth at which the intergranular pores in the soils become saturated with water. When above the ground surface, it is expressed as a surface water body, such as a lake or stream. When below ground, as is usually the case in a desert, the water is still there, but can only be reached through digging or drilling. There are known cases where desert playas have positive water pressure at their surface, (the water table is above the surface), but the water evaporates as fast as it can leak out onto the surface, so no surface water is present.
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