Geologic sections across the Adelaida Quadrangle, California: Supplement 4 from "Geology of the Adelaida quadrangle, California" (Thesis)

This geological investigation covers an area lying across the southern Santa Lucia Mountains in south central California, immediately west of Paso Robles. The land forms of this region are due to structurally controlled erosion which, in most localities, has now produced late mature physiographic surfaces. There are evidences of a Pliocene peneplain, a Pleistocene late mature surface, and vigorous erosion in the present cycle. The sedimentary series, with an aggregate thickness of over 20,000 feet, includes the Franciscan, Knoxville, Chico, Monterey (Vaqueros and Salinas), Santa Margarita and Paso Robles formations. The sediments cover approximately nine-tenths of the area and are all marine in origin except the Paso Robles. Invertebrate fossils, including a large foraminiferal fauna, were found in the Monterey and Santa Margarita beds, but the other sediments yielded practically nothing. Igneous rocks include periodotite altered to serpentine, granite, rhyolite, diabase, granodiorite, dacite porphyry and many basic dikes. All structural lines trend northwest-southeast, paralleling the Santa Lucia Range. Three major fault zones cross the area. They are: normal faults on the west side of the range, vertical ? faults, with predominantly horizontal displacement, just east of the range, and thrust faults in the northeast part of the quadrangle. Compression toward the northeast has caused folding, faulting, and perhaps the differential movement of blocks. Faulting is the controlling factor in the structure. A tectonic relationship between the Pacific Ocean Basin, the California Coast Ranges, the Sierra Nevadas, the Great Basin Region, the Rocky Mountains and the Mississippi Valley is suggested. Early Pliocene deformation formed a range of mountains which were eroded to a peneplain, and later uplift (in two stages) due to faulting produced the masses from which our present mountains have been carved. Quicksilver, in this area always associated with faults and serpentine, is the most important economic mineral product. The ore occurs in silicified and calcitized rock or in sandstone. Other mineral resources of possible economic interest are petroleum, flagstones, lime, asbestos, and chromite