NEW GEOLOGIC MAPPING IN GLEN CANYON NATIONAL RECREATION AREA, SOUTHERN UTAH AND NORTHERN ARIZONA

At 5076 square kilometers, Glen Canyon National Recreation Area in southern Utah and a small part of northern Arizona is one of the largest units in the national park system (in comparison, Grand Canyon National Park encompasses 4926 square kilometers). Lake Powell, around which it is centered, only covers about 13 percent of the recreation area at high lake level. The recreation area actually extends over 300 kilometers and has about as many kilometers of river above the high shoreline of the lake as it does below the high shoreline. The Utah Geological Survey, working in cooperation with the National Park Service, recently completed new and revised geologic maps covering the main part of Glen Canyon National Recreation Area at 1:100,000 to 1:24,000 scales. Some maps were compiled from published sources, while new field mapping was required in other areas. In all areas, the maps were revised to better match the topography of corresponding USGS topographic maps. The maps reflect modern concepts in geologic mapping, including more accurate placement of formation and member contacts, breaking out members in several areas where they had not been mapped previously, and mapping surficial deposits in increased detail to more accurately depict their distribution and depositional environment. The maps were produced as printed (plot-on-demand) and geographic information system (GIS) database files to meet the needs of a variety of map users, and are distributed through the Utah Department of Natural Resources Map and Bookstore. Accurate detailed geologic maps are essential to the management of the fragile desert lands because of their proximity to Lake Powell, which receives about 1.8 million recreation visits per year. Unusually remote lands, limited access, travel restrictions, deep lake-flooded canyons, and rugged river corridors presented unusual challenges to mapping.