U.S. Supreme Court adopts the doctrine of equitable apportionment of benefits for rivers flowing between states.  Kansas v. Colorado, 206 U.S. 46.  The equitable apportionment doctrine is based on the “cardinal rule” of “equality of right” among states.  “Each state stands on the same level with all the rest.”  The Court later explains that “equality of right” refers “not to an equal division of the water, but to the equal level or plane on which all the states stand, in point or power and right, under our constitutional system.”  Wyoming v. Colorado, 259 U.S. 419, 465 (1922).

Seven basin states organize League of the Southwest in Salt Lake City to promote Colorado River development

Congress authorizes the seven basin states to negotiate and enter into an interstate compact providing for the equitable division and apportionment of the Colorado River

The Colorado River Commission is organized at Washington, D.C.

The Fall-Davis Report submitted to Congress recommends construction of the All-American Canal in California and a dam at Boulder Canyon in Nevada

U.S. Supreme Court rules that the doctrine of prior appropriation can be applied between states where each of the states adheres to that doctrine.  Wyoming v. Colorado, 259 U.S. 419.

Colorado River Compact signed in Santa Fe, New Mexico

All states, except Arizona, ratify the Colorado River Compact

Boulder Canyon Project Act approves the 1922 Compact and authorizes construction of the All-American Canal and Boulder Dam (later renamed for President Herbert Hoover)

California enacts the California Limitation Act, agreeing to limit its use of Colorado River water to 4.4 million acre feet per year

President Hoover declares the Boulder Canyon Project Act to be in effect.

Arizona files suit in the Supreme Court against the Secretary of the Interior and the other six basin states seeking to block implementation of the Boulder Canyon Project Act.

Secretary of the Interior asks California to recommend an apportionment of its share of the Colorado River among water users in that state.

The U.S. Supreme Court dismisses Arizona’s action without prejudice, holding that the Boulder Canyon Project Act is a valid exercise of congressional authority and does not purport to abridge any of Arizona’s rights.  Arizona v. California (I), 283 U.S. 423.

California Seven Party Agreement among Palo Verde Irrigation District, Imperial Irrigation District, Coachella Valley County Water District, Metropolitan Water District of Southern California, City of Los Angeles, City of San Diego and County of San Diego establishes their relative priorities to Colorado River water.

Metropolitan Water District of Southern California enters into an amended contract with the Secretary of the Interior for delivery of Colorado River water in accordance with the California Seven Party Agreement.

Imperial Irrigation District enters into a contract with the Secretary of the Interior for delivery of Colorado River water in accordance with the California Seven Party Agreement. Contract also provides that the United States will construct Imperial Dam and the All-American Canal.

Palo Verde Irrigation District enters into a contract with the Secretary of the Interior for delivery of Colorado River water in accordance with the California Seven Party Agreement.

City of San Diego enters into a contract with the Secretary of the Interior for delivery of Colorado River water in accordance with the California Seven Party Agreement.

Arizona seeks to file a complaint in the U.S. Supreme Court to perpetuate testimony for a future action arising out of the Boulder Canyon Project Act to be brought against California and others.

The Supreme Court denies Arizona’s motion.  Arizona v. California (II), 292 U.S. 341.

Coachella Valley County Water District enters into a contract with the Secretary of the Interior for delivery of Colorado River water in accordance with the California Seven Party Agreement.

Arizona petitions to file suit against California in the U.S. Supreme Court, seeking to quiet title to Arizona’s equitable share of the Colorado River and to limit California’s equitable share to no more than 4.4 maf. Arizona also asks for a decree that any other state’s use of Arizona’s equitable share of the Colorado River shall not constitute a prior appropriation or create any right superior to Arizona’s.

The Supreme Court again denies Arizona’s motion, holding that the United States is an indispensable party to any adjudication of the Colorado River but that it cannot be joined without its consent.  Arizona v. California (III), 298 U.S. 558.

Parker Dam is completed.

The seven basin states organize the Committee of Fourteen, comprised of two representatives from each state, to address Colorado River issues

Metropolitan Water District of Southern California begins diverting water through the Colorado River Aqueduct.

Nevada enters into a contract with the Secretary of the Interior for delivery of 300,000 af of Colorado River water.

United States and Mexico enter into a Treaty on the Utilization of Waters of the Colorado and Tijuana Rivers and of the Rio Grande. The Treaty guarantees Mexico 1.5 maf from the Colorado River in a normal water supply year. In the event of a surplus, Mexico is entitled to an additional 200,000 af. In the case of “extraordinary drought or serious accident to the irrigation system in the United States,” delivery of water to Mexico “will be reduced in the same proportion as consumptive uses in the United States are reduced.” United States agrees to construct Davis Dam to regulate deliveries to Mexico under the Treaty.

Arizona enters into a contract with the Secretary of the Interior for delivery of 2.8 maf of Colorado River water.

Arizona ratifies the Colorado River Compact

The Supreme Court retreats somewhat from its ruling in Wyoming v. Colorado, holding that “strict adherence to the priority rule” when equitably apportioning the flow of a river among prior appropriation states “may not be possible.” While priority remains the “guiding principle,” the Court identifies a number of additional factors that may be taken into account. “For example, the economy of a region may have been established on the basis of junior appropriations. So far as possible those established uses should be protected though strict application of the priority rule might jeopardize them.”  Nebraska v. Wyoming, 325 U.S. 589, 618.

Arizona seeks legislation authorizing the CAP. California opposes.

Upper Colorado River Basin Compact signed by Arizona, Colorado, New Mexico, Utah and Wyoming

Senate passes CAP legislation.

CAP legislation dies in House committee.

House Committee on Interior and Insular Affairs indefinitely postpones action on CAP legislation “until such time as the use of the water in the Lower Colorado River Basin is either adjudicated, or a binding, mutual agreement as to the use of the water is reached by the states of the Lower Colorado River Basin.” (The Colorado River Board of California later boasted that it had been “instrumental” in achieving this result.)

Senate passes CAP legislation for the second time.

Arizona files suit against California in Supreme Court to establish its right to Colorado River water.

U.S. Supreme Court grants Nevada’s motion to intervene in Arizona v. California (IV).

U.S. Supreme Court denies California’s motion to join the four upper basin states in Arizona v. California (IV), but joins New Mexico and Utah as lower basin states.

Colorado River Storage Project Act authorizes construction of Glen Canyon, Flaming Gorge, Navajo and Curecanti Storage Units

U.S. Supreme Court decision in Arizona v. California

Reclamation completes Glen Canyon Dam (Lake Powell)

In reaction to the Supreme Court’s opinion, California immediately announces that it will oppose authorization of the Central Arizona Project.

U.S. Supreme Court original decree in Arizona v. California

Western governors establish the Western States Water Council to avoid interstate conflict by developing regional solutions to water problems

Meeting in Washington, D.C., representatives of the seven basin states reach agreement on four general principles:

  • The Lower Basin’s temporary use of unused Upper Basin water will not jeopardize Upper Basin rights.
  • Importation of water from outside the Colorado River basin is essential and pending legislation should authorize construction of works to import at least 2.5 maf.
  • Imported water should be available no later than 1980, although there appears to be sufficient water to meet all needs, including CAP, until the 1990s.
  • Satisfaction of the Mexican treaty obligation should be a national obligation and the first priority for imported water.

Colorado River Basin Project Act authorizes construction of the Central Arizona Project and six Upper Basin projects

U.S. and Mexico enter Minute 242 to the 1944 Treaty addressing salinity of water delivered to Mexico at Morelos Dam

Colorado River Basin Salinity Control Act authorizes salinity control projects above and below Imperial Dam, including the Yuma Desalination Plant

Secretary of the Interior adopts regulations for offstream storage and release of unused apportionment enabling interstate water banking in the Lower Basin

Secretary of the Interior adopts Interim Surplus Guidelines establishing criteria for declaring surpluses in the Lower Basin states

Interim surplus determinations are suspended after California parties fail to complete a quantification settlement agreement by the December 31, 2002 deadline in the Interim Surplus Guidelines.

United States enters into Colorado River Water Delivery Agreement with Imperial Irrigation District, Coachella Valley Water District, Metropolitan Water District of Southern California and San Diego County Water Authority. The agreement memorialized the Secretary of the Interior’s commitment to deliver water to California contractors in accordance with the Quantification Settlement Agreement.

Quantification Settlement Agreement executed memorializing U.S. commitment to deliver water to California

Secretary of the Interior announces her intent to develop guidelines for conjunctive management of Lakes Powell and Mead and shortage sharing in the Lower Basin by December 31, 2007, and initiates a public process toward that end. The Basin States are encouraged to reach agreement.

Basin States submit a Preliminary Proposal Regarding Colorado River Interim Operations, including coordinated management of Lake Powell and Lake Mead and shortage guidelines for the lower basin.

U.S. Supreme Court enters its Consolidated Decree in Arizona v. California

U.S. and Mexico enter Minute 319 to the 1944 Treaty establishing criteria to share in water surpluses and shortages

Environmental pulse flow and base flow, allowed by Minute 319 to the 1944 Treaty, are released through the Colorado River channel in Mexico to start new vegetation for wildlife habitat

The Drought Contingency Plan is passed by all seven states and Congress.