Sir: I have the honor to transmit herewith Bulletin 165, Geology and Mineral Deposits of Barstow Quadrangle, San Bernardino County, California, prepared under the direction of Olaf P. Jenkins, Chief, Division of Mines, Department of Natural Resources. The report is accompanied by detailed colored geologic and economic mineral maps, charts and cross sections, and many other illustrations. The area covered by the report lies in the Mojave Desert and embraces 976 square miles, a 30-minute quadrangle. The mineral deposits described consist of limestone, dolomite, ganister (quartzite), barite, magnesite, pyrophyllite, mica-quartz fillers and ornamental stone such as marble and granite, which are the chief non-metallic minerals of the area; gold, silver, iron, copper, lead, zinc and tungsten, the metallic minerals. The underground water supplies of the area are also discussed as they are related to the geology. The report represents one of the basic geologic map projects of the Division of Mines. It has been prepared by a member of the staff, Oliver E. Bowen, Jr. Included with Bulletin 165 is another report, representing the results of laboratory investigations of some peculiar ceramic materials found in the area. This report is entitled, Thermal Properties of Ceramic Materials From Barstow Quadrangle, California. It has been prepared by Joseph A. Pask, professor of Ceramic Engineering, University of California, in cooperation with Oliver E.Bowen, Jr., of the Division of Mines. Bulletin 165 should be of value in the development of all manner of natural resources found in the area and especially of assistance in the development of the mineral industry in this desert region.