NEW QUATERNARY GEOLOGIC MAPPING IN THE SOUTHERN SAN JOAQUIN VALLEY, CALIFORNIA

The southern San Joaquin Valley (SSJV) is ideally situated to study the impact of Quaternary deformation systems on the margin of a large basin that exhibits the potential for carbon sequestration. New 1:100,000-scale geologic mapping, extending from the Sierra Nevada foothills in the east to the Temblor Range in the west, lends new insights into the Quaternary history of the SSJV. This mapping is the first phase of the California Geological Survey’s Southern San Joaquin Basin 3D Geo Project, which is aimed at assessing the potential for carbon sequestration in the Great Valley Geomorphic Province of California. The map area covers approximately 4,000 sq. mi. northwest of Bakersfield, California, including the Lost Hills Oil Field, the California Aqueduct, highway corridors, and Tulare Lake. Newly acquired lidar and existing aerial photographs were used in compilation and new mapping. For the bedrock geology and Quaternary units on the east side of the SSJV, we compiled previously reported mapping from multiple sources into a uniform map product and refined contact locations through lidar interpretation. On the west side of the SSJV, we improved the detail in the Quaternary mapping by expanding the existing two map units into a total of 11 units based on observed changes in surface morphology, weathering, and topography. This mapping also identified previously unrecognized Quaternary faults along the western margin of the SSJV, where gently east-sloping alluvial fans are cross-cut by NW-SE trending topographic lineaments, often with uphill facing scarps and sometimes collocated with channel truncations. Other faults are expressed as topographic lineaments of older Quaternary units, with younger units ponded against the uphill side. In some cases, the scarps are obscured by younger units like channel deposits or ponded alluvium. Several of these faults are collocated with other geomorphic indicators of uplift like oblong ridges and geologic patterns indicative of anticlines. Our work shows that the Quaternary history of the SSJV is more complex than previously mapped and highlights the benefits of new lidar-based mapping for identifying future paleoseismic studies and contextualizing these structures within the broader plate boundary given their proximity to critical infrastructure.