Unfortunately, Arizona would have a difficult time proving exactly how much of the water they had actually appropriated. The next best thing, then, would be to be able to prove how much water the other Colorado River Basin states believed Arizona had appropriated at the time they ratified the Compact. The problem was that Hoover Dam would not be completed for several years, and the injury to Arizona might not occur for years beyond that, given the underdeveloped use of the Colorado River at the time. This meant that witnesses to the Compact's negotiations would die, their memories would fade, and their notes might be lost or destroyed. It had already been ten years since the Compact was written.
Arizona therefore brought an action in the Supreme Court to allow it to extend process to witnesses, depose them, acquire exhibits, and other evidence in preparation for this potential future litigation. Naturally, California opposed this. Primarily a procedural battle, the case was again dcided by Justice Brandeis.
Explore the 1934 decision in Arizona v. California, 292 U.S. 341.