This digital dataset defines the extent of the alluvial deposits in the Central Valley of California and encompasses the contiguous Sacramento, San Joaquin, and Tulare Lake groundwater basins defined by California's Department of Water Resources. The boundary encompasses an approximate 50,000 square-kilometer region of California. The boundary was used to define the lateral boundary of the area simulated by the transient Central Valley Hydrologic Model (CVHM) (Faunt, 2009). The CVHM is the most recent regional-scale model of the Central Valley developed by the U.S. Geological Survey (USGS). The CVHM was developed as part of the USGS Groundwater Resources Program (see "Foreword", Chapter A, page iii, for details).