This digital data set defines the boundary of the hydrogeologic framework model (HFM) developed by IT Corporation (1996) for the U.S. Department of Energy Underground Test Area Phase I project. The boundary encompasses an approximate 53,000 square-kilometer region which is centered on the Nevada Test Site (NTS) and extends from Death Valley to east of the East Pahranagat Range, and from the Black Mountains to north of Penoyer and the southern part of the Railroad Valleys. The HFM was developed using geologic reports, maps, measured stratigraphic sections, 54 regional interpretive cross sections, approximately 700 lithologic well logs, and geophysical interpretations to define the spatial distribution and composition of 20 hydrogeologic units. The HFM formed the basis of the regional steady-state ground-water flow model of the NTS and surrounding areas developed by IT Corporation (1996b). Belcher and others (2002) integrated the IT Corporation (1996) and the D'Agnese and others (1997) HFM's to produce an HFM for the steady-state flow model of the Death Valley regional ground-water flow system (DVRFS) for the Department of Energy. Source data from the IT Corporation (1996) and the D'Agnese and others (1997) HFM's were subsequently integrated with new geologic interpretations to produce the HFM supporting the transient flow model of the DVRFS (see "Larger Work Citation", Chapter A, for details). References: Belcher, W.R., Faunt, C.C., and D'Agnese, F.A., 2002, Three-dimensional hydrogeologic framework model for use with a steady-state numerical ground-water flow model of the Death Valley regional flow system, Nevada and California: U.S. Geological Survey Water-Resources Investigations Report 01-4254, 87 p., https://pubs.usgs.gov/wri/wri014254 D'Agnese, F.A., Faunt, C.C., Turner, A.K., and Hill, M.C., 1997, Hydrogeologic evaluation and numerical simulation of the Death Valley regional ground-water flow system, Nevada and California: U.S. Geological Survey Water-Resources Investigations Report 96-4300, 124 p., http://pubs.er.usgs.gov/pubs/wri/wri964300 IT Corporation, 1996, Underground test area subproject, Phase I, Data analysis task, volume I-Geologic model data documentation package: Las Vegas, Nev., Report ITLV/10972-181 prepared for the U.S. Department of Energy, 8 volumes, various pagination. IT Corporation, 1996b, Underground test area subproject, Phase I, Data analysis task, volume VI-Groundwater flow model data documentation package: Las Vegas, Nev., Report ITLV/10972-181 prepared for the U.S. Department of Energy, 8 volumes, various pagination.