A 4500-YEAR RECORD OF LARGE FLOODS ON THE COLORADO RIVER IN THE GRAND-CANYON, ARIZONA

A sequence of flood deposits left by the Colorado River in the Grand C anyon, Arizona, provides evidence of at least 15 floods with peak disc harges greater than 5500 m3sec-1 over the last 4500 yr. Ten floods dur ing the last 2000-2300 yr had discharges greater than 6800 m3sec-1. On e flood, 1600-1200 yr ago, had a discharge exceeding 14,000 m3sec-1, a flow rate more than twice the largest gaged flood. This record of flo oding is one of the longest for a major U.S. river, and, combined with the gaged record of twentieth century floods, allows determination of the frequency and history of large floods that have affected key aspe cts of Colorado River geomorphology.