California Division of Mines and Geology Bulletin 182 Geologic Guide to the Merced Canyon and Yosemite Valley, California

In performance of its function as the State's public information bureau on geology, mineral resources, and mineral industries, the Division of Mines and Geology assists the petroleum industry, responsible for two-thirds of California's annual mineral production, in the general area of exploration. This it does by detailed geologic mapping of selected areas and by reconnaissance of large areas on the 1:250,000 scale, and by publication of several series of geologic maps and reports, many of which are useful to petroleum exploration. These are: Mineral Information Service, a semi-popular monthly pamphlet; Annual Report of the State Geologist, Chief of the Division of Mines and Geology; the Bulletin series, on the geology and mineral resources of quadrangles, geologic guides to significant regions, or on statewide commodity surveys; the Special Report series on shorter or more localized subjects; the new County Report series on the mines, mineral resources, and geology of counties; and the State Geologic Map, issued as colored, lithographed, 1:250,000-scale geologic map sheets, each 1 degree in latitude by 2 degrees in longitude.

In planning field trips and a guidebook which would be most interesting and of greatest benefit to the petroleum profession, as well as to the people of California, the committees felt that the greatest effort should be directed toward presentation of geologic features of northern California of direct economic importance to the petroleum industry; and also that our unique scenic geological attractions should not be neglected. The first condition has been satisfied by Bulletin 181, Geologic guide to the gas and oil fields of northern California; the second we hope to meet with this publication, Bulletin 182, Geologic guide to the Merced Canyon and Yosemite Valley, California. The latter book is the result of co-operation between the U.S. Geological Survey, the University of California, and the State Division of Mines and Geology. It consists of four papers by Survey and University authors on the metamorphic and granitic rocks of the western Sierra Nevada, the geomorphology of the area, and on soils of the San Joaquin Valley along the Merced River, followed by continuous road logs from Hayward across the Coast Ranges and northern San Joaquin Valley and through the Yosemite Valley. Route of the trip is by way of Altamont Pass across the Diablo Range and close to the Tracy and Vernalis gas fields of the northern San Joaquin Valley. Those interested in more geology relating to this area and the occurrence of gas are referred to the section Northern San Joaquin Valley, in Bulletin 181, which contains Vernalis gas field, by Charles F. Manlove, Cretaceous geology of the Pacheco Pass area, by Frederick O. Schilling, and Type Panoche group (Upper Cretaceous) and overlying Moreno and Tertiary strata on the west side of the San Joaquin Valley, by Max B. Payne. Bulletins 181 and 182, together, constitute a unit which should give the geologist an adequate geologic background for understanding the occurrence of gas and oil in northern California.

GORDON B. OAKESHOTT
General Chairman, AAPG-SEPM Convention, 1962
and Deputy Chief, Division of Mines and Geology.

San Francisco
January 11, 1962

Frontispiece. Yosemite winter storm, by Ansel Adams. From Portfolio Three (Yosemite Valley), published by the Sierra Club, San Francisco, 1959.