Geology of a Portion of the Santa Ana Mountains, California

Citation

Southwick, Thomas Scott (1929) Geology of a Portion of the Santa Ana Mountains, California. Master's thesis, California Institute of Technology. doi:10.7907/VRF8-M041. https://resolver.caltech.edu/CaltechTHESIS:01042010-084811253

Abstract

In this paper is presented a geologic map of a part of the southern Santa Ana mountains. Studies in lithology were made especially of the Tejon formation. The structure was found to be simple with a few faults which were studied by the writer, especially the Cristianitos and the San Onofre faults. The physiographic and geologic history are discussed. Finally, some clay deposits of economic importance arc described.

The area described in this report comprises about seventy-five square miles in the southern portion of the Santa Ana mountains in Southern California, and embraces parts of Orange and San Diego counties. See Plate I. This area is covered by the south-east corner of the Corona, and the north-east corner of the Capistrano quadrangles, respectively.

The region was studied, at the suggestion of Dr. J. P. Buwalda, in the nature of a research problem requisite to the Master of Science degree. The Santa Ana mountains present many interesting problems, to some of which the writer directed his attention. In this connection, it should be indicated that these problems are to a great extent regional ones, and that a study, even though intensive, can only shed light on these rather than solve them. For this reason, the writer did not hesitate to draw freely upon the information in the several reports on this general region, especially the notably paper by A.O. Woodford. (Woodford, A.O., The San Onofre Breccia – Its Nature and Origin.: Univ. Cal. Publ., vol. 15, No. 7, pp 159-280, 1925). Specific references to these papers will be made throughout the course of this report. An excellent bibliography will be found in Woodford’s paper.

A brief statement of the general geology of this portion of Southern California will perhaps clarify somewhat the following discussions. The Santa Ana mountains are a tilted, seaward sloping mountain block with a very straight and abrupt fault scarp that faces the north-east and overlooks the Perris peneplain. The block is an elevated peneplain with Cretaceous and Tertiary sediments upon its flanks grading into the coastal plain. Farther south, the structure becomes somewhat more complicated due to other mountain ranges, but the same tilted structure predominates.

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