HARTMAN MULTIMEDIA
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HARTMAN MULTIMEDIA
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Orocopia Mountains The Orocopia Mountains are a geological area of
considerable interest in determining the displacement history of the San Andreas
Fault. The rocks exposed in the mountains range in age from
Pre-Cambrian gneiss, which has yielded at least one radiometric age date of
2,400,000 years, to Recent alluvium. Much
of the western portion is composed of the grayish, sometimes greenish Orocopia
schist which has been dated as old as the Pre-Cambrian and as recent as the
Mesozoic. In the eastern section
much of the area is the Oligocene or early Miocene varicolored Diligencia
formation consisting of non-marine conglomerates, sandstones, and breccia as
well as some volcanics. A band
bordered by the Orocopia thrust and the Clemens Well Fault, and consisting of
the gneiss and other rocks, grossly separates the two areas. Of particular interest is the fossiliferous Maniobra
formation, consisting of Eocene marine siltstones and sandstones, which is the
only Eocene rock in the region on the eastern side of the San Andreas Fault. Its
nearest correlate is in the Piru Creek region about 260 kilometers (162 miles)
northwest. The area is riddled with faults. The various colored,
folded strata, which have been uncovered by erosion, form, in places,
spectacular displays. Vegetation on the slopes is sparse and consists of
creosote bush scrub, with occasional cactus gardens. The area supports a typical Colorado Desert fauna,
including the desert tortoise, Gopherus agassizi, which is relatively abundant
here. See also Mecca Hills. Integrity: Several
abandoned mines and some jeep trails are the sole development.
The Butterfield Stage Route passed through the area.
Aside from off-road vehicle damage in some of the washes, much of the
area is virtually pristine. Use: Research,
educational, observational, light recreation. Ref: Crowell,
John, 1975. Geological Sketch of the
Orocopia Mountains, Southeastern Calif., in Crowell, J. C. (ed.) San Andreas
Fault in Southern California, Calif. Div. Mines and Geol. Spec. Rep. No. 118,
pp. 99-110. August 1976
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