Planning Commission Supplemental Materials 11-12-25 (2)

CULTURAL RESOURCES SURVEY REPORT 4400 Black Ave 5 BACKGROUND ENVIRONMENT During the early historic era, the project area was at the border of a seasonal wetland called the Pleasanton Marsh complex to the north and drier grassland to the south. The Pleasanton Marsh complex was one of the Bay Area’s largest freshwater, non-tidal wetlands. It consisted of a variety of intermixed wetland types, which included “many springs and supported a large area of open water, seasonal wetlands, and extensive willow thickets and freshwater marshlands” (Standford et al. 2013: 79). In the project area, the wetlands were composed of wet meadow in the north-northeast and willow thicket (swamp) along the western boundary. The Arroyo del Valle Creek, one of the main contributors to the marsh complex, flowed 600 feet southwest of the project area through the marsh (Thompson and West 1878; Stanford et al. 2013). The grassland was part of a large, varied grassland present in much of the Amador-Livermore Valley. In this part of the Bay Area, oaks were confined mainly to the hillsides and riparian corridors due to soil conditions, and the valley bottom supported a variety of grasses and flowers encouraged by Ohlone land management practices (Stanford et al. 2013: 76-78) PREHISTORY Some of the first significant archaeological work in the San Francisco Bay Area was conducted early in the 20th century when N.C. Nelson recorded and/or excavated over 400 bayside shell mounds (Nelson 1909; Moratto 1984). Data from these excavations and successive projects in the San Francisco Bay, San Joaquin/Sacramento River Delta, and inland sites illuminated regional archaeological sequences and allowed the development of the Central California Taxonomic System (CCTS). The CCTS outlines three main chronological periods (or ‘horizons’) for the Sacramento Delta and San Francisco Bay areas – Early, Middle, and Late, mostly based on evidence from mortuary practices and analysis of stylistic change in burial-associated artifacts. We summarize the Early, Middle, and Late Periods, with the transitions between them, following Hylkema’s (2002) and Milliken et al.’s (2007) approaches. The Early-Middle-Late sequence focuses on the Late Holocene period (after 2000 BCE), since little archaeological information from the Early Holocene is known from the San Francisco Bay Area. In other parts of California, the Early Holocene (8000-3500 BCE) is characterized by mobile foragers using wide-stemmed and leaf-shaped projectile points and large milling slabs (Milliken et al. 2007:114). Given the rise in sea levels in the Middle Holocene, the relatively recent formation of San Francisco Bay, and the presence of constant alluviation in the low-lying areas of the Bay Area, most evidence of the earliest human habitation in the area is likely to be underwater or deeply buried. For the Early Holocene period, therefore, most evidence comes from inland sites: deposits dating from ca. 8000 BCE and burials dating from 5500-5000 BCE were discovered around Los Vaqueros Reservoir in eastern Contra Costa County (Meyer and Rosenthal 1997), and deep deposits from the Metcalf Creek site (CA-SCl-178) in Morgan Hill yielded radiocarbon dates of 8000-6500 years BCE (Hildebrandt 1983; Milliken et al. 2007:114; Jones et al. 2007:130).