GEOLOGIC MAPPING FOR LAND-USE PLANNING--THE U.S. GEOLOGICAL SURVEY'S CENTRAL COLORADO ASSESSMENT PROJECT

The Front Range urban corridor in north-central Colorado, with a population growth of more than 30 percent since 1990, stretches about 350 km from Pueblo in the south, through Denver, north to the Colorado-Wyoming border. Important resource and land-use management issues, especially in the mountainous region west of the urban corridor, include: (1) maintaining the quantity and quality of ground and surface waters, (2) accurate assessment of industrial and mineral resources, (3) environmental effects of abandoned mine lands on National Forest and private lands, (4) geologic hazards, such as landslides and stream flooding, and (5) long-term effects of forest fires on erosion and deposition, all exacerbated by a warming and drying climate. Of particular concern are hundreds of old mines and prospects within the northeast-trending Colorado mineral belt that, due to acid-water and trace-metal contamination, threaten the quality of both surface and ground water. Addressing these and other land-use issues requires accurate and up-to-date geologic maps and related topical data. A major goal of our integrated work is to revise existing geologic mapping and remap poorly understood areas in order to create state-of-the-art, digital databases at a level of detail appropriate for a series of 30’ x 60’ geologic quadrangles in and adjacent to the Front Range. Mapping of the Estes Park and Denver West quadrangles is nearing completion, and work in the Bailey and Fort Collins quadrangles has begun. Future plans are to complete geologic maps for the Pikes Peak, Leadville, and Vail 30’ x 60’ quadrangles. Several topical studies being conducted concurrently with the mapping include: (1) fracture analysis related to ground water flow in several areas in the Front Range (e.g., watersheds in Turkey Creek and Montezuma areas), (2) geochemical characterization of surficial deposits, bedrock, and surface and ground water adjacent to mineralized areas, and (3) climatic conditions during emplacement of large, early and middle Pleistocene debris flows near Boulder. Project personnel are also investigating U-Pb zircon ages and isotopic signatures of various basement rocks to improve understanding of Early and Middle Proterozoic crustal genesis.