Timeline of key Colorado River water use events.
— Summer 1869: John Wesley Powell's expedition navigates the Colorado River and Grand Canyon by boat.
— 1889: International Boundary and Water Commission created between U.S., Mexico. (Spanish: Comisión Internacional de Límites y Aguas).
— Nov. 24, 1922: Signing of the Colorado River Compact. "The Law of the River" outlines the rights of northern and southern basins to each use 7.5 million acre feet of water a year. An acre-foot is about enough to serve two homes annually.
— 1928: Boulder Canyon Project Act: Ratifies 1922 compact, authorizes construction of Hoover Dam and lower basin irrigation facilities. California apportioned 4.4 million acre-feet of water a year; Arizona, 2.8 million acre-feet; Nevada 300,000 acre-feet.
— Sept. 30, 1935: Boulder Dam dedication. Later renamed Hoover Dam
— Feb. 3, 1944: Treaty for the Utilization of Waters of the Colorado and Tijuana Rivers and of the Rio Grande: U.S. commits 1.5 million acre-feet of Colorado River water annually to Mexico.
— 1948: Upper Colorado River Basin Compact: Apportions 7.5 million acre-feet of upper basin water a year. Colorado gets 51.75 percent; Utah, 23 percent; Wyoming, 14 percent; New Mexico, 11.25 percent. Arizona also gets 50,000 acre-feet of upper basin water annually.
— 1956: Colorado River Storage Project Act: Authorizes construction of Glen Canyon, Flaming Gorge, Navajo and Curecanti dams.
— 1973: Minute 242 of the U.S.-Mexico International Boundary and Water Commission: Requires U.S. to reduce salinity of water delivered to Mexico at Morelos Dam in Baja California near Yuma, Ariz.
— 1974: Colorado River Basin Salinity Control Act: Authorizes desalting and salinity control projects including the Yuma Desalting Plant.
— 2010: Magnitude-7.2 Easter Sunday earthquake damages Mexico irrigation systems, prompts temporary Lake Mead water storage agreement.
— Nov. 20, 2012: Minute 319 of the U.S.-Mexico International Boundary and Water Commission signing in Coronado, Calif.
Source: U.S. Bureau of Reclamation, AP research.