West Mojave Plan FEIR/S - Desert Managers Group

Basin and Range province is a geologic term referring to the structure of this province'svalleys (basins) and mountains (ranges) aligned roughly north to south. The province extendsfrom the Wasatch Mountains of Utah to the eastern side of the Sierra Nevada in California. Thispart of North America is a region where the earth's crust has been extended (stretched thinner)from east to west, and mountain ranges in this province are generally bounded by faultsassociated with this thinning and stretching. The planning area north of the El Paso Mountainsand east of U.S. Highway 395 is part of the Basin and Range province. This includes the CosoMountains, the Argus Mountains, the Slate Mountains and their adjacent valleys. The CosoMountains consist largely of igneous/volcanic rocks, including pumice, basalts, cinders andobsidian, and is tectonically active with frequent, very small earthquakes. The Argus and SlateRanges are mostly igneous/granitic rocks, with some volcanic rocks and exposures of limestoneformations. Searles Valley is well known for its deposits of sodium minerals, which are theremnant of a Pleistocene lake that once formed the terminus of the Owens River.The Transverse Range region is one of eastward-trending mountain ranges and valleys.It is so named because this trend is transverse to the generally northwesterly trending features ofsouthern California. The lowlands of the San Bernardino and Los Angeles plains of the easternpart of this region rise abruptly northward to the San Bernardino and San Gabriel Mountains,respectively, two of the most rugged and highest ranges in southern California. The rock units ofthe Transverse Range region may be divided into two main groups, (a) crystalline basementcomplex composed of metamorphic and plutonic rocks, and (b) sedimentary and volcanic rocks.The metamorphic rocks of this complex include, from oldest to youngest, Precambrian gneissand marble, Precambrian Pelona Schist, Paleozoic metasedimentary rocks hosting goldmineralization, and marble/limestone used for cement, specialty fillers and extenders, chickengrit, and aggregate, and Pre-Cenozoic rock (Dibblee, 1970, p. 36).In summary, the age of the rocks within the area ranges from Precambrian to Recent andis characterized by great diversity including marine and nonmarine sedimentary rocks and a widevariety of volcanic and intrusive igneous rocks. The geologic events include those related toplate collision, metamorphism, and faulting. This diversity of rock types, long history of igneousactivity, and the complex structural and geomorphic development of the region have resulted inthe formation of a wide variety of mineral assemblages and their concentration to form the oredeposits that are present in the study area. Characteristics of favorable geologic environments, or“permissive terrains”, for the potential occurrence of mineral resources in the area are discussedin an unpublished U.S. Geological Survey report (Tosdal, et al, 1992, 21 p.).Soils: Soil surveys have been completed by the United States Department of Agriculture,Natural Resource Conservation Service on less than half of the planning area. Published soilsurveys include the Southeastern Part of Kern County, San Bernardino County Mojave RiverArea, Fort Irwin National Training Center, Edwards Air Force Base, and the Marine Corps AirGround Combat Center Twentynine Palms. Because of the large area within the MojavePlanning Area and incomplete soil survey coverage, general soil information will be used andextrapolated in areas that are not covered by soil surveys for this analysis.Chapter 3 3-56