This digital dataset defines the model grid and altitudes of the top of the 10 model layers and base of the model simulated in the transient hydrologic model of the Central Valley flow system. The Central Valley encompasses an approximate 50,000 square-kilometer region of California. The complex hydrologic system of the Central Valley is simulated using the USGS numerical modeling code MODFLOW-FMP (Schmid and others, 2006), which estimates dynamically integrated supply-and-demand components of irrigated agriculture as part of the simulation of surface-water and ground-water flow based on MODFLOW-2000. This application is referred to here as the Central Valley Hydrologic Model (CVHM) (Faunt, 2009). Utilizing MODFLOW-FMP, the CVHM simulates groundwater and surface-water flow, irrigated agriculture, land subsidence, and other key processes in the Central Valley on a monthly basis from 1961-2003. The total active modeled area is an approximately 20,334 square-miles on a finite difference grid comprising 441 rows, 98 columns. Slightly less that 50 percent of the cells are active. It has a uniform horizontal discretization of 1x1 square mile and is oriented parallel to the valley axis, 34 degrees west of north (Faunt, 2009).The thickness of model layers is derived by sequentially subtracting the altitudes of the uppermost to the lowermost model layers. Most model layers range in thickness from 15 to more than 300 meters, and thickness generally increases with depth (Faunt, 2009). The upper 3 model layers are used to simulate the relatively shallow flow through basin-fill sediments. Layers 4 and 5 are used to represent the Corcoran Clay Member of the Tulare Formation. The lower 5 layers are used to simulate the confined deeper portion of the basin-fill sediments. 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).