Geology of the Southern Part of the Red Mountain Quadrangle, California

Citation

Ahlroth, Carl Wilhelm (1938) Geology of the Southern Part of the Red Mountain Quadrangle, California. Bachelor's thesis, California Institute of Technology. doi:10.7907/E3F3-D756. https://resolver.caltech.edu/CaltechTHESIS:12212009-151213006

Abstract

An area of about twenty square miles in the southern half of the Red Mountain Quadrangle, Los Angeles County, California, was mapped geologically in the spring of 1938. The area lies within the Transverse Ranges Province of California, and comprises the following rocks: a pre-Cambrian mica schist (Pelona schist), continental sediments of Oligocene (?) (Sespe formation) and lower-upper Miocene (Mint Canyon formation) age, and marine sediments of upper Miocene age (Modelo). The Sespe is overthrust over the Pelona schist and the Mint Canyon. The Mint Canyon lies with a depositional contact upon the Pelona schist and is overlain unconformably by the Modelo which overlaps it to the west.

The area has undergone several periods of rejuvenation during Quaternary times, the uplift not being accompanied by tilting. Remnants of the old land surface and stream terraces at various levels indicate that before uplift the area was in late maturity of the physiographic cycle; now it is in a youthful stage of development.

The main structural features are the Sespe overthrust, folds trending northeast-southwest, and a well developed flow cleavage and shear joint system in the schist. Forces of a static nature have affected the area at one time, as shown by the flow cleavage in the schist, but the most recent, dominant force acting in the area is considered to be compressive, non-rotational, inclined below the horizontal, and acting in a southwest direction. Its attitude is approximately N10°E.

The area investigated and herein described is situated in the northwestern part of Los Angeles County and in the southwestern part of the San Gabriel Mountains. It comprises the southern half of the Red Mountain Quadrangle, having as its eastern and western limits, 118°30’ and 118°36’ west longitude and as its northern and southern limits, latitudes of 34°33’ and 34°30’ respectively. The area mapped contains about twenty square miles. It is about forty-five miles north-west of Los Angeles and about nine miles north of Saugus. The area lies within the reserves of the Angeles National Forest.

The area is easily reached by automobile, for there are excellent paved roads from all outlying districts which lead to Saugus. The main highway from Los Angeles to Saugus is U.S. 99, but there are others equally good. In addition a branch of the Southern Pacific railroad passes through Saugus. The only unpaved road to be encountered is a good, gravel road in San Francisquito Canyon.

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