RESULTS OF RECENT STATEMAP GEOLOGIC MAPPING IN WESTERN COLORADO

Colorado Geological Survey (CGS) began mapping the geology of 7.5-minute quadrangles in 1993, under the auspices of the STATEMAP grant program. Funding is provided by the U.S. Geological Survey (from the National Cooperative Geological Mapping Program) and is matched by the State of Colorado (from severance taxes paid on the production of natural gas, oil, coal, and metals). We have mapped 101 quadrangles since the program's inception.

In western Colorado, our recent mapping efforts have focused on areas near Delta (9 maps), Grand Junction (2 maps), Meeker (3 maps) and Craig (5 maps). The areas are similar in that the outcropping strata are predominantly Cretaceous to Paleocene in age, and they are located along major river valleys. The purpose of the mapping is to provide geologic information that could be used for land-use, geologic-hazards, and natural-resource assessments.

This poster session will highlight major findings from each of the mapping areas. An important, general result is that we have been able to map sedimentary formations in unprecedented detail, particularly the Mancos Shale (up to 12 subunits) and the Mesaverde Group (up to 17 mapping units). We collect marine invertebrate fossils to add to the knowledge of Cretaceous biostratigraphy in the region. Similarly, we map the Quaternary deposits in great detail and assess their depositional environments and geomorphology. This allows us to recognize different types and ages of gravel deposits, correlate the deposits, and reconstruct Pleistocene-to-Holocene river histories. Dating methodologies (for example, radiometric, radiocarbon, luminescence, and pollen) have been employed for stratigraphic control and to refine age constraints for the Cretaceous/Paleocene boundary, Miocene-Oligocene volcanic rocks, and the Quaternary alluvial deposits. Finally, the mapping has revealed details about local structure. Many of these folds and faults have not been previously mapped.