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City of Pleasanton—Hidden Canyon Residences and Preserve Geology, Soils, and Seismicity Draft EIR 3.6-16 FirstCarbon Solutions https://adecinnovations.sharepoint.com/sites/PublicationsSite/Shared Documents/Publications/Client (PN-JN)/2148/21480016/EIR/3 - Draft EIR/21480016 Sec03-06 Geology.docx most of the last century it was regarded as a formation. Most recently it has been treated as a group containing the Claremont Shale and Sobrante Sandstone which were classified as formations. For this analysis, the Monterey Formation will be considered a formation which contains the Claremont Shale and Sobrante Sandstone members. While the project site is not located within an area of deposition except for the Quaternary alluvium along Devany Creek, the region was prehistorically uplifted by tectonic processes from the Pacific Ocean and further deformed by the North American and Pacific Plate boundary. As such, invertebrate fossils such as clams, mollusks, and shells may be present in the Monterey Formation (or Group) and its associated members. The UCMP provides the Locality Search, an online database that displays a list of vertebrates, invertebrates, microfossils, and plant localities associated with its institution. The data distributes each locality’s ID and name along with the County of discovery, the geologic period and epoch, storage age, and sometimes the related rock formation and taxonomy units and specimen associated with the fossil locality. Although the UCMP Locality Database Search does not provide the absolute location of localities within a project area, the associated names may indicate approximate locations. According to the preliminary analysis using the UCMP Locality Search, at least five vertebrate fossils associated with the Miocene Claremont Member (or Formation) and Monterey Formation (or Group) (Tm) have been discovered in Alameda County with three found during the excavation of the fourth bore for the Caldecott Tunnel in Oakland. These three have a storage age of Clarendonian within the North American Land Mammal Ages (NALMA). Numerous Monterey Formation (or Group) (Tm) localities within the County have produced invertebrate fossils. A records search request was sent to the UCMP on March 6, 2025, to obtain complete information on the fossil localities listed within its repository that are associated with the rock units and geography of the project area to determine the potential of ground-disturbing activities during construction of the proposed project to disturb and uncover significant paleontological resources. The UCMP completed its records search on March 25, 2025, and confirmed the project site to be underlain by Miocene rock units which classified the Monterey Formation as the Monterey Group. The records search indicated no fossil localities to be uncovered on the direct project site within the Monterey Formation (or Group). However, the UCMP identified three vertebrate localities, and 13 invertebrate localities uncovered from Miocene rock units northwest of the project site along I-580. Of these localities, two vertebrate localities were uncovered approximately 3.5 miles west to northwest from the project site within the Sobrante Sandstone member of the Monterey Formation and yielded five specimens with taxon consisting of Mammalia, Chondrichthyes, and Allodesmus. The invertebrate localities were uncovered from the Claremont Shale and Sobrante Sandstone members, the Monterey Formation (or Group), and the San Pablo Formation and consisted of several mollusks including those from the Class Bivalve, Gastropod, and Scaphopod. Although most of the surficial conditions on the project site are overlaid by rock units with low paleontological potential consisting of colluvium and residual soils due to their recent deposition and relatively young age, excavations exceeding the depths of the low potential rock units may disturb the Monterey Formation (or Group) and the Claremont Shale member (or Formation). These rock units consist of marine sedimentary rock units matching the SVP Standard Procedures definition as having high paleontological potential, and have previously contained fossil localities yielding vertebrates