What does it mean if one-third of irrigated acres in California go out of production? Well, depends on your perspective. First, it does not mean the end of agriculture in California, because two-thirds of irrigated agriculture would persist. That’s 6 million acres of irrigated agriculture, which is rather a lot.
Does it mean that your fruits and veggies will get more expensive? Does it mean that non-Californians will never have an almond again? Should you be hoarding wine? I don’t know. That depends on how the transition happens. The only thing that looks inevitable to me is that meat and dairy will become much more expensive. Relatively cheap feed, like alfalfa and silage, is the underpinning for cheap meat and dairy. I don’t see how those can remain cheap, nor how meat&dairy can withstand the way resource consumption intensifies with each step up the food chain.
Will the agricultural economy collapse? It doesn’t have to. Some two-thirds of it will remain, probably where the water resources were richest in the first place. The Sacramento Valley, the coastal valleys, Yolo, the northeast side of the San Joaquin Valley will be able to keep farming. Places that are poor now will become poorer until they are abandoned or find new industries.
Would retiring lands really suck for the people who are now farming them? It could. Again, it depends on how it happens. But many of the problems caused by farms going out of production are problems of poverty. Those can be addressed with things that may be more available than water, like re-training for other careers or monetary support or funding for re-location.
What about the empty barren land, with poisonous salt dirt-devils swirling everywhere? That’s the Salton Sea, you guys. In the San Joaquin Valley, it would return to scrub. Not every inch of land has to be farmed.
On the public record 
I can tell you what it does to other property owners, when downstream ranchers get water rights to the headlands of a river and take advantage of those rights, diverting almost all the water out of it,into their own reservoir, in violation of the rules of the SWRCB ordering them to leave 5 cfs flowing through the river. The South Fork Irrigation District is under these regulations. For the past three years, they have again violated these regulations and this year, have almost totally drained the river down to 1.75 cfs to 3.5 cfs. In doing the right thing, we spoke with members of the SFID who advised the gauges were giving faulty readings. We spoke with the USGS and obtained readings performed when there were calibrations of the gauge. The manual readings were consistent with the ongoing readings of the gauges, which indicated gauge accuracy. Fish cannot live in 1.75-3 cfs of water. We cannot exercise our riparian water rights as a result of others not following state laws. The new chief enchilada of the McGarva Ranch, Ross McGarva couldn’t address the issues, as he claimed he had no knowledge of water rights. Instead, he personally attacked the individuals who asked him to stop this practice and claimed he was going to do what he had to do in order to water his cattle. Swenson’s people agreed to look at it and resolve it. Likely Land and Cattle had no response when phone calls and emails were sent. The question…if the trees on my land are dying from no water, can I go downstream and steal someone else’s trees so I can make a profit from selling trees? That is exactly what is happening here. Droughts are tough, but it doesn’t mean everyone else but the rancher has to suffer so they do not…that is not the Christian way….Ross McGarva and the rest of the seven families at the South Fork Irrigation District.
Outdoor cannabis doesn’t need much water, right? If so, there’s your replacement crop right there.
Pot uses a lot of water: http://m.motherjones.com/blue-marble/2015/03/marijuana-farming-drought-salmon-california.
Pot probably uses about the same amount as the crop it would replace. Pot is draining creeks up in the north because it is an entirely new load on their system. But I don’t believe pot is especially thirsty compared to other crops.