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).

League of the Southwest is organized by the seven basin states at Salt Lake City to promote the development of the Colorado River.

U.S. 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 is submitted to Congress, recommending the construction of the All-American Canal and a dam at Boulder Canyon.

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, N.M., by representatives of the seven basin states.

California, Colorado, Nevada, New Mexico, Utah and Wyoming ratify the Compact.

The Boulder Canyon Project Act (BCPA) authorizes construction of Hoover Dam and the All-American Canal.  The Act also approves the Colorado River Compact and apportions Colorado River water among the lower basin states as follows:  4.4 million acre-feet (maf) to California; 2.8 maf to Arizona; 300,000 acre-feet to Nevada.  BCPA is contingent on all seven basin states ratifying the Compact; if all of the states did not ratify the Compact within 6 months, the BCPA would still become effective if six of the basin states, including California, ratified it and if California, by legislative act, agreed irrevocably and unconditionally with the United States and for the benefit of the other basin states to limit its consumptive use of Colorado River water to 4.4 maf.

California enacts the California Limitation Act, agreeing to limit its use of Colorado River water to 4.4 maf.

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 issues related to the Colorado River.

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  is signed by Arizona, Colorado, New Mexico, Utah and Wyoming.  The Compact grants Arizona 50,000 af of Colorado River water from the Upper Basin and divides the remaining Upper Basin supply as follows:  Colorado, 51.75%; New Mexico, 11.25%; Utah, 23%; and Wyoming, 14%.  The Compact also creates the Upper Colorado River Commission.

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 is signed into law, authorizing construction of Glen Canyon, Flaming Gorge and Navajo Dams, among other projects.

Glen Canyon Dam is completed.

The Supreme Court releases its opinion in Arizona v. California (IV), 373 U.S. 546.  The Court concludes that it was fear that development in California would lead to that state being first in time and first in right to Colorado River water under the doctrine of prior appropriation that led the basin states to seek authority from Congress to negotiate a compact for the “equitable division and apportionment” of Colorado River water.  But the 1922 Colorado River Compact failed to divide water among the states, leaving Nevada and Arizona to worry that California would rely on prior appropriation doctrine to acquire the majority of the river’s supply.  To resolve that issue, Congress “provided its own method for allocating among the Lower Basin States the mainstream water to which they are entitled under the Compact,” and in the process effected a “complete statutory apportionment” of the river.  In giving the Secretary of the Interior the authority to contract for Colorado River water, Congress necessarily also gave the Secretary the power to allocate water among the states and to decide which users in each state would get water.  The Court noted that an earlier version of the Boulder Canyon Project legislation “limit[ed] the Secretary’s contract power by making the contracts ‘subject to rights of prior appropriators.’  But that restriction, which preserved the law of prior appropriation, did not survive.”  Thus, the Court concluded that the Secretary’s discretion is not confined by the law of prior appropriation, in the way that it is by present perfected rights under section 6 of the BCPA.  Although the Court recognized the Secretary’s obligation to respect present perfected rights as of the date of the BCPA, it expressly rejected California’s contention that each state’s share of water in shortage be determined by the judicial doctrine of equitable apportionment or by the law of prior appropriation.

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

The Supreme Court issues its decree in Arizona v. California (IV), 376 U.S. 340.

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 (CRBPA) is signed into law, authorizing construction of the Central Arizona Project and six upper basin projects, including Animas-La Plata.  The CRBPA directs the Secretary to develop a plan for augmenting the Colorado River supply.  It also makes satisfaction of the Mexican Treaty a national obligation that is to be the first obligation of any Colorado River augmentation project.

Secretary of the Interior adopts Criteria for Coordinated Long-Range Operation of Colorado River Reservoirs (commonly known as the Long-Range Operating Criteria or LROC) in compliance with §602 of the CRBPA.  The LROC establishes a “minimum release” of 8.23 maf annually from Lake Powell.

United States and Mexico enter into Minute 242 to their 1944 Treaty governing the Colorado River.  Under Minute 242, the United States agreed to adopt certain salinity control measures—chief among them the construction and operation of the Yuma Desalting Plant—to effect a “permanent and definitive solution” to the international salinity problem on the Colorado River.

Colorado River Basin Salinity Control Act is signed into law, authorizing construction of the Yuma Desalting Plant and other “necessary works” to implement Minute 242.

Secretary of the Interior adopts regulations providing for Offstream Storage of Colorado River Water and Development and Release of Intentionally Created Unused Apportionment in the Lower Division States, which enable interstate water banking in the lower basin.

Secretary of the Interior publishes Interim Surplus Guidelines that establish criteria for declaring surpluses in the lower basin through 2016, provided California water users meet specified targets for reducing that state’s consumptive use to 4.4 maf annually.

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.

Quantification Settlement Agreement executed among Imperial Irrigation District, Coachella Valley Water District and Metropolitan Water District of Southern California.

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.

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, 547 U.S. 150, more than 53 years after the case was filed.

Basin States sign Agreement Concerning Colorado River Management and Operations.  The agreement was transmitted to the Secretary on April 30, 2007, along with proposed interim guidelines and related agreements.

Secretary of the Interior issues Record of Decision on Colorado River Interim Guidelines for Lower Basin Shortages and the Coordinated Operations for Lake Powell and Lake Mead.  The decision closely tracks the Basin States proposal.