Geologic Map of the Crestmore Quarries, Riverside Co., California: Supplement 2 from "The geology and mineralogy of the limestone deposits at Crestmore, Riverside County, California" (Thesis)

This report describes the work done in an area roughly seven square miles in extent. More specifically it includes all, or parts of, sections 31, 32, 33 and 34, T.1.S.,R.5 W.,S.B.B. and M., and of sections 2, 3, 4, 5, 8, 9 and 10, T.2.S.,R.5 W.,S.B.B. and M. Crestmore lies on the extreme lobe of the Jurupa Mountains, an east west range roughly eight miles long and three miles wide. This range parallels the front of the San Gabriel Mountains and rises above the flood plain of the Santa Ana River in the manner of a typical "inselberg". The cement plant and the limestone quarries of the Riverside Cement Company are located at Crestmore. In addition it is a station on an interurban line. Hence the locality is accessible to the geologist and mineralogist both by trolley and by way of good paved highways. Quarrying operations were started at Crestmore some seventeen years ago. The material was first used for cement, road metal, and sugar refining. With the increased value and demand for cement the quarrying operations were given over entirely to cement materials. Mineralogical interest was first aroused when a specimen of blue calcite with monticellite and xantophyllite were sent to A. S. Eakle. The first publication appeared in 1914 (1) and since then numerous papers have been published by A. S. Eakle, W. F. Foahag, A. F. Rogers and others. The purpose of the present investigation was to study the general geology and determine the origin of the minerals associated with the limestone and the other rooks of the area. The economic aspects of the deposits were also investigated. The mapping done in the Crestmore quarries was on a scale of 1' = 100' on a map kindly furnished by the Riverside Cement Company. The hills to the east of the quarries were mapped on a portion of the U.S.G.S. San Bernardino Quadrangle, originally of the scale of 1:62500, but which was photographically enlarged to a scale of 1:31260. A light plane table and a Brunton compass were used in determining locations. Besides the fact that the climate is of the semi-arid type, common for Southern California, this particular district is the center of strong winds. In the winter, these blow from the Mohave Desert southward thru the Cajon Pass. In the summer the prevailing winds come from the coast thru Santa Ana Canyon. The highest and lowest point in the area are 2000 feet and 900 feet respectively, the relief in general averages less than this. Regional drainage flows to the southwest into the Santa Ana River. The underbrush is not thick and is burned over in a large part. As a consequence of this and of the steep relief, exposures are generally good. The quarries offer an excellent opportunity to collect fresh samples. Near the cement plant the rocks have been covered with dust and have been glazed in such a manner that recognition of rock types is often rendered difficult. The writer wishes to acknowledge the help given by Mr. Rene Engel under whose supervision this work was conducted. He wishes to thank the officials of the Riverside Cement Company. Mr. John Treanor, Mr. G. A. Beckett, and Mr. Earl MacDonald, for their permission to make a geologic map of the quarries. Mr. Thomas Mullan, chemist for the Riverside Cement Company, has very generously made numerous analyses for the author and has collected samples for him. Mr. C. A. Robotham of the Mining Department of the Riverside Cement Company has made many helpful suggestions.