The alluvial forms of the rivers that drain the Colorado Plateau are a product of the water and sediment load that tributaries deliver to the trunk streams. Where the Green and Colorado Rivers cross structural barriers, narrow canyons have been incised. In the steep terrain adjacent to many of these canyons debris flows occur in the catchment basins of tributaries and deliver coarse sediment to the mainstem river corridor. Over time, debris flow deposits have aggraded in trunk stream valleys and created landforms known as debris fans. The sizes of these debris fans are related to the accommodation space available for fan formation. Lithologic variation in the layer-cake stratigraphy of the Colorado Plateau has led to varying valley widths. Tributary catchment, debris fan, depositional site, and mainstem river characteristics are examined over the 156-kilometer reach of the Green River through Desolation and Gray Canyons. Desolation and Gray Canyons provide some of the widest valley widths and resultant debris fan areas on the Colorado Plateau.