This raster layer contains the average monthly precipitation levels in inches for December 1981-2010. This dataset incorporates a conceptual framework that uniquely addresses the spatial scale and pattern of orographic precipitation. The original PRISM dataset covered the United States. This is a California-only version subsetted from the original data set and converted to California Teale Albers NAD83 using bilinear interpolation by the California Department of Fish and Game (CDFG) at 800m resolution. The grid units are presented in inches with floating point. Care should be taken in estimating precipitation values at any single point on the map. Precipitation estimated for each grid cell is an average over the entire area of that cell; thus, point precipitation can be estimated at a spatial precision no better than half the resolution of a cell. Accuracy of this data set is based on the original specification of the Defense Mapping Agency (DMA) 1 degree digital elevation models (DEMs). The stated accuracy of the original DEMs is 130m circular error with 90% probability. The Parameter-elevation Regressions on Independent Slopes Model (PRISM) Climate Group works on a range of projects, some of which support the development of spatial climate datasets. These PRISM datasets provide estimates of the basic climate element of precipitation (ppt), or the Daily total precipitation averaged over a month for both rain and melted snow. These datasets are modeled with PRISM using a digital elevation model (DEM) as the predictor grid and provide baselines describing average monthly precipitation between 1981 and 2000 to be used for display and/or analyses requiring spatially distributed monthly or annual precipitation. Grids were modeled on a monthly basis. Annual grids were produced by averaging (temperatures) or summing (precipitation) the monthly grids.