There’s several kinds of corn, but if we’re comparing silage it’s 26 tons / acre vs 7 tons / acre for alfalfa. https://www.nass.usda.gov/Quick_Stats/Ag_Overview/stateOverv... Corn yields are normally measured in terms of grain, but it’s worth remembering the rest of the plant still has value when considering efficiency.

But, the reality is completely eliminating California’s water problems is easy on a legal and technical level but not a political one. There is little incentive to let water flow into the ocean so CA is always going to sit right on the edge of a significant issue.