The San Luis Obispo Valley Groundwater Basin, DWR Bulletin 118 Basin No. 3-09 is situated in the San Luis and Edna Valleys in central to southwest San Luis Obispo County. A rise in bedrock south of the San Luis Obispo Airport has created two separate subsurface drainage systems or subbasins (i.e., San Luis Valley and Edna Valley). The basin overlies an area of approximately 12,700 acres (19.9 square miles) and is part of the Central Coast Watershed. The Edna Valley Subbasin (approximately 4,700 acres) is entirely within unincorporated San Luis Obispo County, while the San Luis Valley Subbasin (approximately 8,000 acres) includes both unincorporated County and the City of San Luis Obispo.