In 1902 the passage of the Reclamation Act and its mandate for the federal government to build dams for irrigation in the West created a need for accurate topographical surveys and geological studies of the rivers where the dams would be built. By 1920 the US Geological Survey (USGS) and other agencies had surveyed the easily accessible stretches of the Colorado river and its main tributaries. The remaining segments had yet to be charted because they were located in deep canyons that were coarsed with rapids and reachable only by boat.