MAPPING THE COLORADO FRONT RANGE: ASSESSMENT OF GEOLOGIC RESOURCES AND ENVIRONMENTAL ISSUES

The Front Range urban corridor in Colorado, centered on Denver and including a large part of the mountainous region west of the plains, is one of the fastest-growing regions in the western U.S. The population in this area has grown more than 30 percent since 1990, resulting in a number of pressing resource and land-use management needs. To help assess these needs, the U.S. Geological Survey is currently completing four 30' x 60' (1:100,000-scale) state-of-the-art digital geological maps for areas in and near the Front Range, extending from the Wyoming border to about 20 north of Colorado Springs. From north to south, these maps are the Fort Collins, Estes Park, Denver West, and Bailey sheets. In addition, seven 7½' (1:24,000-scale) quadrangles in this map area will be published. Preparation of these maps involves reevaluation of existing geological mapping and considerable new mapping, particularly in more poorly understood regions. The maps include the geologic history of the region and discussions of the mineral deposits and geologic hazards. An emphasis is placed on surficial mapping, commonly neglected in past works, and the text for several of these maps includes an in-depth discussion of the Quaternary history of the region. An enhanced understanding of the crustal evolution of the Front Range basement rocks is provided by new U-Pb and Sm-Nd isotopic studies. These maps provide new focused tools to help resolve a variety of resource and land-use issues, including: (1) geologic hazards, such as landslides and stream flooding, (2) the quantity and quality of both ground and surface waters in mountain-recharge environments, (3) the Precambrian and Phanerozoic basement framework and its relationship to mineral deposits, (4) surficial processes, especially those related to changing climate over time, (5) industrial and mineral resources, including aggregate, ornamental stone, limestone, coal, oil, and natural gas, (6) the effects of increased recreational land use in the Front Range region, such as erosion of roads and trails, (7) the long-term effects of forest fires on erosion and sedimentation, and (8) mitigation of abandoned mine lands. The latter three items are of particular concern for the management of our National Forests.