The Sprague River drains 4090 square kilometers in south-central Oregon before flowing into the Williamson River and upper Klamath Lake. In cooperation with the U.S. Fish and Wildlife Service, the USGS and University of Oregon conducted a study to evaluate channel and floodplain processes for the 131 km of the Sprague River and its major tributaries, including the lower 20 km of the South Fork Sprague River, the lower 16 km of the North Fork Sprague River, and the lower 62 km of the Sycan River. The study involved multiple analyses, including assessments of historical channel change, riparian and floodplain vegetation, and surficial geology. To support these analyses, digital floodplain and channel maps were prepared from historic notes, maps, and aerial photos to depict channel and floodplain conditions at different times between 1866 and 2005. The geospatial database of current and historic channel and floodplain conditions will also enable evaluation of long-term trends pertaining to aquatic and riparian habitat conditions.