DOI: 10.5066/p96wfs3t
title: Digital hydrogeologic framework model of the Upper Colorado River Basin, western U.S.

description: This digital dataset was created as part of a U.S. Geological Survey hydrologic resource assessment and development of an integrated numerical hydrologic model of the hydrologic system of the Upper Colorado River Basin, an extensive region covering approximately 412,000 square kilometers in five states: Wyoming, Colorado, Utah, Arizona, and New Mexico. As part of this larger study, the USGS developed this digital dataset of geologic data and a three-dimensional hydrogeologic framework model (3D HFM) that define the elevation, thickness, and extent of seven hydrogeologic units in the Upper Colorado River Basin. The hydrogeologic setting of the Colorado Plateau consists of thick Paleozoic, Mesozoic, and Cenozoic aquifers, predominantly sandstone and limestone, that are separated by regionally extensive confining units of fine-grained siliciclastic rocks, all overlain by generally thin Quaternary sediments. Based in part on the need to maintain consistency with previously published USGS hydrogeologic studies in the region (Craigg, 2001; Freethy and Cordy, 1991; Geldon, 2003; Glover and others, 1998), seven hydrogeologic units (HGUs) were modeled across the Upper Colorado River Basin: (1) TIPCG, Tertiary Intrusions and Precambrian Granite, a confining unit that includes crystalline igneous and metamorphic rocks of all ages; (2) PZAU, Paleozoic aquifer unit, including Mississippian and Pennsylvanian carbonate rocks and Permian sandstones and conglomerate; (3) CMCU, the Chinle-Moenkopi confining unit, including red Triassic fine-grained sandstone, siltstone and shale; (4) MZAU, Mesozoic aquifer unit, including thick, dominantly eolian Triassic and Jurassic sandstones of the Glen Canyon Group and overlying dominantly fluvial and alluvial sandstones and shales of the San Rafael Group; (5) MCU, Mancos confining unit, including thick sections of Cretaceous marine shale; (6) KTAU, Cretaceous-Tertiary aquifer unit, including marginal marine to continental siliciclastic sections with locally thick Cenozoic volcanic rocks; and (7) QAU, Quaternary alluvial unit, consisting predominantly of alluvial sediment along modern washes and drainages. Surface and subsurface data compiled include a digital elevation model, geologic contacts shown on geologic maps, reported formation tops from oil and gas wells, and structure contour and isopach maps. Input surface and subsurface data have been reduced to points that define the elevation of the top of each hydrogeologic units; these point data sets serve as digital input to the 3D framework model. Surfaces representing the elevation of the top of each hydrogeologic unit were created through standard interpolation methods of input data points using two-dimensional horizon gridding software. Data were interpolated using faults as two-dimensional boundaries that acted as a barrier to information flow during interpolation. Resultant HGU elevations were mapped to an x, y array of 1-km polygonal cells in geographic information systems (GIS) software. Each cell within the array was assigned attributes representing the top elevation thickness of each hydrogeologic unit. This polygonal cellular array is essentially a ?flattened?, 2.5D (multiple z values stored at each x,y coordinate) representation of the digital 3D HFM, defining the elevation, thickness, and extent of each of the 7 HGUs at every cell centroid. The digital dataset includes a geospatial database that contains the following data elements: (1) a digital hydrogeologic map and map of fault locations for the model domain, (2) compiled digital input data to the 3D HFM for each hydrogeologic unit; (3) the 3D HFM, stored as interpolated elevation and thickness of the seven hydrogeologic as attributes of an XY array of polygonal cells; and (4) elevation surfaces of each HGU interpolated as triangular irregular networks (TINs) and extruded volumes (?multipatch?). The spatial data are accompanied by non-spatial tables that describe the sources of geologic information, a glossary of terms, a description of model units, and a Data Dictionary that duplicates the Entity and Attribute information contained in the metadata file. Spatial data from the geodatabase are also saved in shapefile format and nonspatial tables from the geodatabase are also provided in CSV format.