The Colorado River Compact of 1922 forms the foundation for Western water law. It allocated specific amounts of the river’s water for the Lower Basin (Arizona, California and Nevada) and the Upper Basin (Colorado, New Mexico, Utah and Wyoming), as well as setting aside how those two Basins should split the water allocated to Mexico. Importantly, it obligates (a legal term) a minimum amount of water that should be delivered to the Lower Basin: 75 million acre-feet per decade.