GEOLOGIC MAP SERIES OF THE DENVER BASIN BETWEEN GREELEY AND COLORADO SPRINGS, COLORADO

In 1998 the Denver Museum of Nature of Science commenced the Denver Basin Project as a multi-disciplinary effort to study the geology of the Upper Cretaceous and Lower Tertiary sedimentary rocks of the Denver Basin. Simultaneously, the Colorado Geological Survey began aggressively mapping along the Front Range under the STATEMAP program in order to understand the architecture of the Denver Basin aquifers in outcrop. Both organizations began to integrate surface geology with subsurface data to characterize strata that form a critical aquifer system supplying water to a rapidly growing region. Recognizing similar goals, the organizations collaborated in preparing a combined set of surface and subsurface maps of an area covering over 7,000 square miles east of the Front Range, Colorado. The product combines information from over 25 geologic maps with a subsurface data base containing 2,951 geophysical well logs.

A bedrock geologic map of the Upper Cretaceous to Lower Tertiary sedimentary rocks of the Denver Basin , five structure maps of selected stratigraphic horizons, and four isopach maps covering selected stratigraphic intervals were generated. Structure maps include the Niobrara Formation top, a marker bed near the top of the Pierre Shale, the Fox Hills Sandstone top, the Laramie Formation top, and the Dawson Group D1 Sequence top. Isopach maps define thicknesses of the Pierre Shale, the Fox Hills Sandstone, the Laramie Formation, and the Dawson Group D1 Sequence. Three cross sections illustrate heterogeneity in sedimentary rock types across the basin and three paleogeographic maps show the depositional patterns for Denver Basin at selected time intervals.

All maps were made using a digital three-dimensional data base and have been cross-checked to maintain internal consistency. This nested suite of maps provides a robust 3D interpretation of the basin. Structure maps were intersected with a ten meter resolution digital elevation model (DEM) to constrain outcrop traces where concealed beneath Quaternary cover. Where the Quaternary cover exceeds 200 feet, thickness values were subtracted from the original DEM to better delineate subcrop patterns.