SU0015801 - Laserfiche WebLink

Home Browse Search

4 Environmental Analysis 4.7 Geology, Soils, and Paleontological Resources 4.7 GEOLOGY, SOILS, AND PALEONTOLOGICAL RESOURCES This discussion identifies and evaluates potential impacts related to geology, soils, and paleontological resources in relation to the Griffith Energy Storage Project (Project). The Project site includes the proposed facility and the generation tie (gen-tie) line corridor (including both the Applicant portion and the portion for which Pacific Gas and Electric [PG&E] will be responsible). The discussion below provides a description of the physical and regulatory setting, the criteria used to evaluate significance of impacts, the methods used in evaluating these impacts, and the results of the impact assessment. San Joaquin County (County) received no scoping comments regarding geology, soils, and paleontological resources. 4.7.1 Existing Conditions 4.7.1.1 Regional Geology The Project site, including the gen-tie corridor, is located on the eastern edge of the Coastal Ranges geomorphic province, not far from the boundary with the Great Valley geomorphic province. The Coastal Ranges province includes a number of named mountain ranges, including the Diablo Range east of the San Francisco Bay Area. The Project site and gen-tie corridor are situated on the eastern flank of the Diablo Range, where the topography is rolling hills and the local relief is just over 170 feet from the highest to lowest point. The Great Valley geomorphic province is a mostly intact (i.e., with limited deformation in the central areas), asymmetric structural trough that has been filled with two thick sequences of sediment deposits. These deposits range in age from the Quaternary to the Jurassic period (CGS 2002). The two sequences are the older Mesozoic Great Valley Sequence and the younger Cenozoic Great Valley fill. The Diablo Range portion of the Coastal Ranges province extends from the northern boundary of Contra Costa County to Watsonville in the south, a length of over 80 miles. The topographic features have resulted from the long history of plate movement and collision along the Pacific Coast and subsequent folding and faulting (Bartow 1991). 4.7.1.2 Local Geology The available sources for geologic mapping in the vicinity of the Project location include Dibblee (1980), Wagner et al. (1991), and the general online map provided by the California Geological Survey (CGS) (Jennings et al. 2010). They characterize the local geology as quite complex, resulting from plate movements and mountain building to the west that has resulted in various geologic "assemblages" (large, fault-bounded blocks containing a unique stratigraphic sequence of different rock units). The assemblages are characterized as primarily Tertiary and overlying older sedimentary rocks from the Cretaceous Great Valley sequence. The assemblage identified in the Project area consists of a poorly consolidated silt, sand, and gravel unit (Pliocene age), Neroly Sandstone (a blue sandstone of Miocene age), and Cierbo Sandstone (a light gray to white quartz sandstone of Miocene age). All of these units overlie various siltstones, mudstones, and sandstones (Great Valley members of Cretaceous age). Griffith Energy Storage Project 4.7-1 Tetra Tech/SCH 2022120675 Draft Environmental Impact Report August 2023