Geomorphic basemap for the Colorado River in Grand Canyon, Arizona - May 2009

These spatial data represent alluvial deposits of the Colorado River and tributary deposits adjacent to the Colorado River in Grand Canyon National Park. The map covers the river corridor from Lees Ferry, Arizona to the confluence with Diamond Creek 225 miles (362 km) downstream. The alluvial deposits of the Colorado River are mapped as either sand or gravel based on surface composition and the sand deposits are further subdivided based on sandbar type (Schmidt, 1990; Mueller and others, 2018). The alluvial deposits are also subdivided based on whether they are bare sediment or covered by dense riparian vegetation. The tributary deposits consist primarily of tributary debris fans, which are coarse-grained material transported by tributary flash floods and debris flows (Webb and others, 1989). The source data for creating the alluvial and tributary deposit features were orthorectified, 25-cm resolution, color aerial photographs (described in Davis, 2012). The map units, represented as vector polygon features, were hand digitized on-screen with these images as a background base layer. The map depicts conditions at the time the base images were collected, which was May 2009 while the Colorado River was flowing at a steady flow of approximately 8,000 ft3/s (227 m3/s). In addition to mapping the deposits exposed above the water surface, the wetted channel was also mapped and subdivided based on general hydraulic characteristics. The primary distinction was between portions of the channel with only downstream flow at 8,000 ft3/s and portions of the channel with lateral flow separation zones, or eddies. The alluvial, channel, and tributary fan deposits are also grouped based on the debris-fan eddy complex unit (Schmidt and Rubin, 1995).