The U.S. Geological Survey (USGS) has collected or incorporated over 20,000 physical property measurements into an ASCII database. These data are primarily from the western U.S. and Alaska and are dominated by granitic rock samples from the Sierra Nevada (compiled by Sikora and others, 1991), but also include a range of other commonly found rocks types. The data include density, magnetic susceptibility, and in some cases, remanent magnetic properties. Density data for more recently collected samples include grain, dry-bulk, and saturated-bulk density measurements. Sample locations are in the North American Datum of 1927 (NAD27) and elevations are in the National Geodetic Vertical Datum of 1929 (NGVD29). These physical property data are particularly useful for potential-field (gravity and magnetic) investigations and modeling of regional crustal structures and subsurface geology as an aid to understanding geologic framework. The ASCII formatted data release includes physical property data, a data dictionary describing the data fields, and a rock dictionary describing the rock types.