9628 - Laserfiche WebLink

Home Browse Search

Introduction This report is an important milestone in the effort by the Secretary of the Interior to implement the Grand Canyon Protection Act of 1992 (GCPA; title XVIII, sees. 1801-1809, of Public Law 102-575), the most recent authorizing legislation for Federal eflorts to protect resources downstream from Glen Canyon Dam. The chapters that follow are intended to provide decision makers and the American public with relevant scientific information about the status and recent trends of the natural, cultural, and recreational resources of those portions of Grand Canyon National Park and Glen Canyon National Recreation Area affected by Glen Canyon Dam operations. Glen Canyon Dam is one of the last m~or dams that was built on the Colorado River and is located just south of the Arizona-Utah border in the lower reaches of Glen Canyon National Recre- ation Area, approximately 15 mi (24 km) upriver from Grand Canyon National Park (fig. I). The information presented here is a product of the Glen Canyon Dam Adaptive l\tJanagement Program (GCDAtvIP), a federally authorized initiative to ensure that the primary mandate of the GCPA is met through advances in information and resource management. The U.S. Geological Survey's (USGS) Grand Canyon Monitoring and Research Center (GCMRC) has responsibility for the scientific monitoring and research efforts for the program, includ- ing the preparation of reports such as this one. The Study Area Carved from the Earth by the Colorado River, Grand Canyon is a natural wonder that is "absolutely unparalleled throughout the rest of the world," as President Theodore Roosevelt said upon seeing it for the first time in 1903 (Roosevelt, ca. 1905, p. 369). Consid- ered one of the world's most spectacular gorges, Grand Canyon exhibits a depth of more than 6,720 ft (2,048 m) at its most extreme in Granite Gorge (Annerino, 2000). The colorful strata of the canyon's walls also reveal an invaluable record of the Earth's geologic his- tory dating back to the 1.84-billion-yr-old rock forma- tions found at Elves Chasm, which are the oldest rocks known in the Southwestern United States (Beus and Morales, 2003). President Woodrow Wilson signed the