Geology of a Part of the Southwestern Portion of the San Gabriel Mountains

Author: Cogen, William Maurice

Year: 1931

Degree: Bachelor's thesis

Advisor: Unknown, Unknown

Committee Member: None, None

Option: Geology

DOI: 10.7907/BFQX-F624

Abstract

The region is in the southwestern portion of the San Gabriel Mountains, north of Los Angeles, California.

Stratigraphically it is composed of a section of Neogene rocks with some up-faulted older rock. The normal sequence as represented here is: Upper Modelo, unconformity; Pico, conformity; Saugus, angular unconformity; Quaternary terraces. The basement rock, composed largely of para-gneiss, schist and intrusive granite, has been faulted up from below. Its age is pre-Miocene, possibly pre-Jurassic.

The structure of the region is characterized by faults of the dip-slip vertical or steeply normal type.

Geologically the history of the region is: invasion of the sea during Miocene time, deposition of the Modelo formation, broad uplift and subsequent denudation; faulting at the opening of the Pliocene, a second incursion of the sea, deposition of the Pico formation; orogenesis north of the region here described followed by withdrawal of the sea in Upper-Pliocene time, deposition of the Saugus formation (Piedmont Deposit); active faulting and orogenesis at the close of the Pliocene; continuous erosion with short resting stages during the Quaternary.

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