One quarter of all the water used in California is used to grow Alfalfa. The total value of the annual alfalfa crop is about $750 million, compared to the state's entire agricultural industry of $45 billion (i.e. it is about 1.5% of the value produced), and the state's entire economy of $1800 billion (it contributes 0.04% of the state GDP) - cities run on water too.
The only reason that alfalfa growing is profitable is that taxpayers are paying for the growers water. The alfalfa plantations pay as little as 10% of the actual cost of delivery, and furthermore have guaranteed access to the water. This is under a 1902 law to encourage family farms and were limited to 160 acre farms - but over time lobbying drove that up to the un-small size of 960-acres, and today the subsidy is given to huge corporate farms that amalgamate holdings of scores of "farms" that exist only on paper, with no families to be seen.
As with mid-west farm subsidies, benefits once handed out long ago for reasons that became irrelevant generations ago just seem impossible to shut off.