NEW MAP PROVIDES INSIGHTS ON THE GEOLOGY OF SOUTHEAST UTAH AROUND GLEN CANYON NATIONAL RECREATION AREA

The Utah Geological Survey, with support and cooperation of the National Park Service, recently completed a new composite geologic map of Glen Canyon National Recreation Area (GCNRA) and vicinity. Centered around Lake Powell (impounded behind Glen Canyon Dam), the map covers an area of approximately 8000 km² in southeastern Utah and northernmost Arizona and extends more than 300 km along the Colorado, San Juan, and Green Rivers. GCNRA is approximately 5000 km², about 13% of which is covered by water. Recreational visits of approximately 2 million person-days per year create diverse and challenging issues for the Park Service, many of which involve managing and preserving the geologic and paleontologic resources. In addition to lands within GCNRA, the map covers important nearby uranium districts; world class vertebrate, invertebrate, and floral fossil localities; and known and potential coal, oil, and gas fields and exploration targets. The new geologic map consists of eleven parts that were completed through new mapping or extensive revision of old maps at scales ranging from 1:24,000 to 1:100,000, and then compiled into a large GIS database. The new map improves placement of formation, member, and surficial deposit contacts, shows new members in several areas, improves placement of fold axes and other structural features, provides new information on thicknesses and thickness trends, includes detailed unit descriptions, and has yielded new insights into faults and fault swarms, lithology and facies changes, landslides and slumps around the lake margins, and surficial deposits and processes. Most of the individual map parts are available as plots, plot files, and GIS data through the Utah Department of Natural Resources Map and Bookstore and Utah Geological Survey website. The composite GIS database is in review for final release. Remote rugged canyons, extensive cliffs, restricted access, flooded canyons, and fluctuating lake levels presented unusual challenges to mapping.