A study was made of the open literature on the geologic structure of the Basin and Range Province of the western United States. Based on this study, an attempt was made to derive a model of a typical basin for use in estimating the seismic ground motion characteristics of alluvial basins in the designated MX deployment area. Among the topics investigated are dimensions and structure of an average basin and characteristic seismic velocities in the basin interiors. In addition, many of the basins are expected to show significant variations from a typical structure and these variations are discussed.