in 1934, Arizona called the state National Guard and militia units to the California border to protest the construction of Parker Dam and California's diversions from the Colorado River.

The Law of the River said California could use surplus Colorado River water if any was to be had. For decades, California had become accustomed to living off of that surplus. But with the settlement of Arizona v. California, the days of surplus were numbered. The deal cleared the way for the construction of the Central Arizona Project (CAP). Its canals stretched 336 miles from Lake Havasu (ironically, the reservoir Moen’s guardsmen tried to block) uphill to Phoenix and Tucson.

On paper, Arizona’s share of water from the main stem of the Colorado all along had amounted to 2.8 million acre feet of water per year. But until the completion of the CAP, it had no way to use it.

In the 1980s, Arizona’s use only topped 2 million acre feet once. In the 1990s, that went up to seven of ten years. Since then, thanks to the CAP, it has been taking close to its full allotment every year. 18

California had been living off of Arizona’s extra water since the beginning. But with the completion of CAP, it became clear to everyone that California needed to reduce its consumption from the  5 million-plus annual acre feet it had been taking to the 4.4 million acre feet allotted by the Law of the River. The Supreme Court’s decision in Arizona v. California made that clear, Interior Secretary Gale Norton told members of the Association of California Water Agencies in November 2002. 19

“I am enjoined by the Supreme Court Decree from delivering water to California beyond its 4.4 million acre-feet allocation unless surplus water is available or there is unused water from Arizona or Nevada. Until recently, the lack of demand in other states allowed California to obtain significant amounts of Colorado River water. This scenario is changing today,” Norton said.