Digital subsurface data of Paleozoic rocks in the Upper Colorado River Basin in Wyoming, Utah, Colorado, Arizona, and New Mexico from USGS Regional Aquifer System Analysis

The Upper Colorado River Basin has a drainage area of about 113,500 square miles in western Colorado, eastern Utah, southwestern Wyoming, northeastern Arizona, and northwestern New Mexico. In the 1980’s and 1990’s, the Upper Colorado River Basin was a study area under of the U.S. Geological Survey's Regional Aquifer-System Analysis (RASA) program (Sun and Johnston, 1994; Sun and Weeks, 1991). The objectives of the RASA program for the Upper Colorado River Basin were to provide regional assessments of major aquifer systems by providing quantitative assessments of the occurrence, movement, and availability of water stored in rock formations that underlie the basin/watershed. These assessments included: (1) the classification of stratigraphic sequences into those intervals that constitute aquifers and those that constitute confining beds; and (2) the generation of maps that portrayed the areal extent of aquifers, aquifer thickness, and overburden thickness. These studies generated a large body of subsurface geologic information as part of the regional aquifer analyses, some of which are captured in this digital data release. Aquifer systems in consolidated rocks in the Upper Colorado River Basin have been grouped into three major subdivisions of sedimentary rocks; in descending order: (1) Tertiary-rock aquifers, (2) Mesozoic-rock aquifers, and (3) Paleozoic-rock aquifers (Taylor and others, 1983; 1986). Within each aquifer group, rocks are further divided into aquifers and confining units on the basis of lithology, depositional environment, and hydrologic characteristics (Glover and others, 1998; Freethy and Cordy, 1991; Geldon, 2003). In a report describing consolidated-rock aquifers of Paleozoic age, 7 hydrostratigraphic units were defined, four aquifers and three confining units (Geldon, 2003). The hydrostratigraphic units of Paleozoic age are locally exposed around the margins of uplifts and in deeply-incised canyon; they occur widely in the subsurface of the Upper Colorado River Basin study area, except in parts of the Uinta, Wind River, and Uncompahgre uplifts where they have been removed by erosion. These hydrostratigraphic units are part of the stratigraphic sequence of Paleozoic rocks that has a total thickness of more than 5,000 ft. This digital dataset contains spatial datasets corresponding to the contoured subsurface maps of Paleozoic rock units produced by the U.S. Geological Survey's Regional Aquifer-System Analysis (RASA) of the Upper Colorado River Basin (Geldon, 2003). The data define the thickness, extent, nomenclature, and facies characteristics of principal hydrostratigraphic units of Paleozoic age in the basin. The digital data describe the following hydrostratigraphic units: the Flathead aquifer, the Gros Ventre confining unit, the Bighorn aquifer, the Elbert-Parting confining unit, the Madison aquifer (consisting of two zones, the Redwall-Leadville zone, and the Darwin-Humbug zone), the Four Corners confining unit (consisting of the Belden-Molas subunit and the Paradox-Eagle Valley subunit), and the Canyonlands aquifer (consisting of three zones, the Cutler-Maroon zone, the Weber-de Chelly zone, and the Park City-State Bridge zone). Contoured thickness and lithology data for each unit are contained in line features classes within a geodatabase; unit extents, facies extents, and formation nomenclatural extents are represented as polygon feature classes. Both types of data are also saved as individual shapefiles. Nonspatial tables define the data sources used, terminology, and the stacking hierarchy and component geologic formations of each the of hydrostratigraphic units.