Geology of Part of the Adelanto Hills. Report on the Geology of the Puente Hills

Citation

Haffner, Bernhard K. and Wasem, Richard (1940) Geology of Part of the Adelanto Hills. Report on the Geology of the Puente Hills. Bachelor's thesis, California Institute of Technology. doi:10.7907/K1QH-J834. https://resolver.caltech.edu/CaltechTHESIS:12222009-152143529

Abstract

Geology of Part of the Adelanto Hills:

The Adelanto Hills are a low range of folded limestone, situated about five miles northwest of Adelanto, California. The limestone is a dark blue finely crystalline, roughly bedded type, which has been hydrothermally altered in places to a white crystalline limestone, or to a fine grained highly altered brown limestone. The main igneous rock outcrops in the south part of the area and is a light colored, coarse grained granodiorite body that apparently has been faulted into place. A complimentary association of several fine grained, dark colored granodiorite intrusions and numerous pegmatite dikes occurs in the northern part of the area. Several large light colored acidic dikes intrude the limestone and their relationships to the other igneous rocks cannot be determined, with the exception that they are earlier than the pegmatite. The alteration of the blue limestone to the white limestone is due in part to the cutting of the area by the acid dikes. Hydrothermal solutions controlled to some extent by igneous contacts, the bedding of the blue limestone and possibly by faults, are responsible for the rest of the alteration. The area is cut by a large fault trending N65W and by numerous smaller faults trending about N2OW. The structure on either side of the main fault is roughly parallel. The mineralization of the area is mainly a contact metamorphic type, the ore minerals being lead, zinc and silver. Oxidation has resulted in some secondary enrichment, especially of silver. Some scheelite is mined at the present time from a contact zone between porphyry and limestone.

Report on the Geology of the Puente Hills:

The area mapped consists of one and two thirds square miles known as the Puente Hills. The Hills are located directly east of the town of Puente and are about fifteen miles south-east of Pasadena. The purpose of the mapping was to give a student geologist some experience in mapping and interpreting a structure of folded sediments. Approximately ten days was spent in the field completing the mapping. The method used was a Brunton Compass traverse with a U.S.G.S. topographic map.

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