> California and the other Mexico-bordering states have so much ag in the middle of the desert because...

... the arable land is flat, sunny, cheap and the government allocated more than all of the Colorado River flow[0] into irrigation systems for them. [1][2]

[0]https://crsreports.congress.gov/product/pdf/R/R45546

[1]https://www.iid.com/water/water-transportation-system/colora...

[2]https://www.cap-az.com/about-us/background

There are lots of Mexicans working in ag in Central Washington state and even in Ontario, Canada. Its climate/weather driven not proximity.

The labor situation is a factor but the arid environment helps with pests and California is basically the ideal environment to grow a lot of things, once you irrigate it. Compare photos of Georgia peaches to California ones and the difference is obvious.