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 Mesozoic age, 10 hydrostratigraphic units were defined, five aquifers and five confining units (Freethy and Cordy, 1991). The hydrostratigraphic units of Mesozoic age occur throughout the Upper Colorado River Basin study area, except in parts of the Uinta, White River, and San Juan uplifts where they have been removed by erosion. These hydrostratigraphic units are part of the stratigraphic sequence of Mesozoic rocks that has a total thickness of more than 8,000 ft. The sandstones of Mesozoic age are the most areally extensive and the thickest bedrock aquifers in the Upper Colorado River Basin. This digital dataset contains spatial datasets corresponding to the contoured subsurface maps produced by the U.S. Geological Survey's Regional Aquifer-System Analysis (RASA) of the Upper Colorado River Basin (Freethy and Cordy, 1991). The data define the thickness and extent of principal hydrostratigraphic units of Mesozoic age in the basin. The digital data describe the following hydrostratigraphic units: the Chinle-Moenkopi confining unit, the Navajo-Nugget aquifer, the Carmel-Twin Creek confining unit, the Entrada-Preuss aquifer, the Curtis-Stump confining unit, the Morrison aquifer, the Morrison confining unit, the Dakota aquifer, the Mancos confining unit, and the Mesaverde aquifer. Contoured thickness data for each unit are contained in line features classes within a geodatabase; unit extents are represented as polygon feature classes. Both types of data are also saved as individual shapefiles. Nonspatial tables define the data sources used, and the stacking hierarchy and component geologic formations of each the of hydrostratigraphic units.