The majority of California's water usage is going to beef and dairy. They are large producers of animal feed which are heavy water users. Per liter, dairy milk requires 628.2 L of freshwater vs almond milk requiring 371.46 L of freshwater. And if you use something like oat milk instead that gets you to 48.24 L

https://ourworldindata.org/environmental-impact-milks

One graph even has California's animal feed water usage so large it actually goes off the chart at 15.2 million acre-feet of water (it is distorted to make it fit as it notes). For some comparison, the blue water usage of animal feed is larger than all of almonds water usage of ~2 million acre-feet of water

https://pacinst.org/wp-content/uploads/2013/02/ca_ftprint_full_report3.pdf#page=25

This is true across the American West as a whole

Correspondingly, our hydrologic modelling reveals that cattle-feed irrigation is the leading driver of flow depletion in one-third of all western US sub-watersheds; cattle- feed irrigation accounts for an average of 75% of all consumptive use in these 369 sub-watersheds. During drought years (that is, the driest 10% of years), more than one-quarter of all rivers in the western US are depleted by more than 75% during summer months (Fig. 2 and Supplementary Fig. 2) and cattle-feed irrigation is the largest water use in more than half of these heavily depleted rivers

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1064&context=wffdocs