TENNYSON, MARILYN E., and WILLIAM R. BEEMAN, U.S. Geological Survey, Denver, CO

ABSTRACT: California: A Digital Compilation in Progress

A geologic map of the Santa Maria 30 x 60 minute quadrangle is being compiled as part of the cooperative Southern California Areal Mapping Project of the U.S. Geological Survey and the California Division of Mines and Geology. Geologic maps of various vintages and scales were photoreduced and traced to make a preliminary composite. To make a final digital version, tracings of the component maps are being scanned and imported into ARC/INFO. ALACARTE, a menu interface for ARC/INFO, is used to edit and tag linework, to label polygons, and to make color plots of the map.

The map centers on the Santa Maria basin, floored by rocks of the Franciscan Complex, Coast Range ophiolite, and Great Valley sequence. Around the margins of the basin, great thicknesses of Mesozoic and Paleogene sedimentary rocks are present beneath upper Oligocene to lower Miocene nearshore sandstone and bathyal mudstone. In the central part of the basin, lower Miocene nonmarine conglomerate and sandstone shed from uplifted blocks along basin-forming faults are present locally. Siliceous basinal mudrocks of the middle Miocene to early Pliocene blanket much of the region. Uppermost Miocene to Quaternary marine and nonmarine sections record filling of the basin and emergence of folded and faulted blocks.

Young, large folds occupy the central part of the basin. A northern anticlinal trend (Casmalia-Orcutt) is separated from the Santa Maria Valley syncline to the north by north-verging reverse faults. A south-dipping fault in Los Alamos Valley thrusts the north limb of a southern anticlinal complex (Lompoc-Purisima) over the south limb of the Los Alamos syncline. The geometry and offset history of most of the faults transecting the region are poorly know, and there are several incompletely resolved differences between traces of major fold axes and faults as mapped by different workers.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.