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Preliminary geologic map of the Black Mountain area northeast of Victorville, San Bernardino County, California

December 23, 2006

The Black Mountain area is in the Mojave Desert about 20 km northeast of Victorville, California. The geology of this area is of interest primarily for its excellent exposures of the early Mesozoic Fairview Valley Formation, a sequence of weakly metamorphosed sedimentary rocks including a thick, commercially important unit of limestone conglomerate that has been mined for cement at Black Mountain Quarry for several decades. Recent geochronologic work has shown that the Fairview Valley Formation is probably of Early Jurassic age. This preliminary geologic map of the Black Mountain area depicts the stratigraphic and structural relations of the Fairview Valley Formation and the associated rocks, most notably the overlying Sidewinder Volcanics of Early(?), Middle, and Late(?) Jurassic age. The map is based on new field studies by the author designed to clarify details of the stratigraphy and structure unresolved by previous investigations. The map is considered preliminary because the ages of some geologic units critical for a satisfactory understanding of the stratigraphic and structural framework remain unknown.

The map area also includes a segment of the Helendale Fault, one of several faults of known or inferred late Cenozoic right-lateral displacement that make up the Eastern California Shear Zone. The fault is marked by aligned northeast-facing scarps in Pleistocene or older alluvial deposits and the underlying bedrock units. Relations in the map area suggest that right-lateral displacement on the Helendale Fault probably does not exceed 2 km, a conclusion compatible with previous estimates of displacement on this fault based on relations both within and outside the Black Mountain area.

Publication Year 2006
Title Preliminary geologic map of the Black Mountain area northeast of Victorville, San Bernardino County, California
DOI 10.3133/ofr20061347
Authors Paul Stone
Publication Type Report
Publication Subtype USGS Numbered Series
Series Title Open-File Report
Series Number 2006-1347
Index ID ofr20061347
Record Source USGS Publications Warehouse
USGS Organization Western Earth Surface Processes