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gaging records from which flow and sediment transport have been estimated (U.S. Department of the Interior, 1995). Witb the exception of Bright Angel Creek (fig, I), the small tributaries below the dam are ungaged. Previous estimates of sediment yield from these tributaries range from zero to the yield from a major gaged tributary with a drainage area equivalent to the total drainage area of all ungaged tributaries. A combination of fluvial and hillslope processes occurs in small tributaries in Grand Canyon, making estimates of sediment yield complicated. Sediment-yield estimates must consider the contri- butions of streamflow, which occur annually in most tributaries, as well as debris flow (Webb and others, 1989). In addition to their importance as sources of fine-grained sediment, the small trib- utaries create and maintain debris fans and rapids on the Colorado River (Powell, 1895; Hamblin and Rigby, 1968; Dolan and others, 1974; Howard and Dolan, 1981; Kieffer, 1985). These tributaries transmit large boulders in debris flows (Cooley and others, 1977; Webb and others, 1989), and reworking of debris fans creates a pool-rapid configuration that stores fine-grained sediment along the Colorado River (Howard and Dolan, 1981; Schmidt and Graf, 1990; Schmidt and Rubin, 1995; Webb, 1996). Debris flows occur in 736 tributaries of the Colorado River in Grand Canyon between Lee's Ferry and Diamond Creek, Arizona, By supplying boulders that exceed the competence of regulated discharges in the river, debris flows also directly control the navigability of the Colorado River, affecting the more than 20,000 whitewater enthusiasts who use the Colorado River for recreation each year (Stevens, 1990), Under- standing the sediment contribution of debris flows over long and short periods of time is important to future adaptive management of the riparian ecosystems and recreational resources of Grand Canyon, Debris flows periodically contribute relatively large volumes of sediment to the river. The hundreds of debris fans that have accumulated along the Colorado River directly control the formation and stability of most sand bars (Schnudt, 1990; Schmidt and Graf, 1990; Schmidt and Rubin, 1995). Therefore, a better understanding of debns flows and the amount of sediment yield from ungaged tributaries is useful to understand trends in the highly regulated sediment budget of Grand Canyon. Development of a sediment budget for the Colorado River through Grand Canyon requires an estimate of long-tenn sediment yields for both coarse and fine particles from hundreds ofungaged tributaries. Estimating these sediment yields depends on estimates of debris-flow frequency and magnitude for as many tributaries as possible. Because the river removes only the finer particles from debris-flow deposits, sediment-yield esti- mates also require knowledge of the particle-size distributions of those debris flows that reach the river. Increased knowledge of debris flow and main stem processes in Grand Canyon will contri- bute to future efforts to operate Glen Canyon Dam in ways that minimize downstream impacts, This report presents the total sediment yield and sand delivery rates for the ungaged tributaries, which previously have been unknown or assumed parts of the sediment budget for the Colorado River, Purpose and Scope The purpose of this report is to estimate the total sediment yield and sand delivery from ungaged tributaries in each of six reaches between Glen Canyon Dam and upper Lake Mead reservoir at the Grand Wash Cliffs (fig, I), This includes the entire drainage area between Glen Canyon Dam and upper Lake Mead reservoir except for the four largest tributaries, These estimates are based on an evaluation of both the debris-flow and streamflow components of sediment yield by multiple techniques. As a secondary objective, we evaluate the potential influence of climatic variability on sediment input in the light of historical climatic fluctuations. This study was funded in cooperation with the Bureau of Reclamation, as part of the Glen Canyon Environmental Studies Program, and the Grand Canyon Monitoring and Research Center. Acknowledgments The authors thank many individuals who helped with the field and office work that led to this report. These individuals have been cited in other publications, including Melis and others (1994), 2 Sediment Delivery by Ungaged Trlbutarlas of the Colorado River In Grand Canyon