This report provides a regional overview with the general public in mind: it also contains detailed background that will benefit more technical users. It is a compilation of the most recent geologic mapping and interpretations focusing on groundwater occurrences in the various geologic formations found in the area. It was funded by the CGS through its Severance Tax and Colorado General Operational Funds. Digital PDF/GIS/ZIP download. OF-17-01D
An online map — ON-OF-17-01 Geology and Groundwater Resources of Mesa County, Colorado — is also available.
Includes report with text, tables, figures, and appendices
Geologic map plates:
Water quality and type map plates:
GIS Data folder
Contains OF-17-01_MesaCo.mpk map-package file
From the Introduction:
Mesa County is the fourth largest county in Colorado and has the largest population of the 28 counties on Colorado’s Western Slope region. Census figures reveal that the population has doubled between 1990 and 2010. A majority of the county (72%) is public land, with the remainder generally housing the population in 15 communities. There are two cities and four towns with municipal water systems, though recent growth tends to be in unincorporated areas that are reliant on groundwater (wells) for domestic water.
The county is located within the Colorado Plateau physiographic province, characterized by high mesas cut by river canyons, dry gullies and washes, and the beds of intermittent streams. Down cutting by the Colorado and Gunnison Rivers has created the Grand Valley, in which many of the cities and towns are located. There is about a 5,000 foot elevation difference between the Grand Valley and the top of the basalt capped Grand Mesa, located to the east.
The county can be structurally divided into three primary geologic features: the Paradox basin to the southwest, the Piceance basin to the northeast, and the Uncompahgre Plateau separating the two. The Uncompahgre Plateau, also referred to as the Uncompahgre Uplift, is a northwest-southeast trending structural arch with bounding faults on both sides. It is cored with Precambrian igneous and metamorphic rocks, typically only exposed in canyons, the largest of which is the Unaweep Canyon. The Grand Valley abuts the north flank of the Uncompahgre Plateau, along the southern edge of the Piceance basin.
The geology of Mesa County encompasses nearly the entire geologic time scale. Most time periods have rock exposures at the land surface, except for the Cambrian through Mississippian sedimentary rocks. These are only present in deeper portions of the Paradox and Piceance basins where they truncate against the sides of the Uncompahgre Uplift. Overlying much of the bedrock are Quaternary unconsolidated sediments, including alluvial aquifers and terraces, glacial deposits near Grand Mesa, and mass wasting deposits. Based on differences in hydrologic properties, aquifers and confining units in Mesa County can be grouped into three general categories: 1) crystalline-rock aquifers, 2) sedimentary bedrock aquifers and confining units, and 3) unconsolidated Quaternary deposits. Within these categories, there were 15 mapped hydrogeologic units.