 Navajo Dam was authorized by Congress in the Colorado River Storage Project Act of April 11, 1956, which also authorized Glen Canyon Dam and numerous irrigation and power projects along the Green River, Gunnison River and other tributaries.The initial authorization for Navajo Dam did not include the Navajo irrigation project, which was authorized much later, in June 1962, along with the San Juan-Chama diversion project.Preparatory work at the Navajo Dam site started on October 8, 1956 with archaeological excavations of Native American sites along the canyons and bottom lands of the San Juan River; however, these investigations were limited in scope and only preserved a handful of artifacts from the area.