Colorado River too much of the lower basin allotment; in 1944 a compromise was reached in which Arizona would get a firm allocation of , but only if California's allocation was prioritized during drought years. These and nine other decisions, compacts, federal acts and agreements made between 1922 and 1973 form what is now known as the Law of the River. On September 30, 1935, the United States Bureau of Reclamation (USBR) completed Hoover Dam in the Black Canyon of the Colorado River. Behind the dam rose Lake Mead, the largest artificial lake in the U.S., capable of holding more than two
Steamboats of the Colorado River shared information about the conditions on the river above them. Robinson piloted the "Explorer" above the point reached by Johnson into the Black Canyon of the Colorado, where they struck a rock that damaged the boat, 40 miles above where Johnson reached. Ives named that rock "Explorer's Rock". While the "Explorer" was being repaired by his engineer, Ives, Robinson and the boat's mate, took their skiff over the next two days farther up the river exploring up through the Black Canyon and beyond to the vicinity of Fortification Rock. Next day, they went two miles farther to Las Vegas Wash,