There is a minimum wage in California. $10.50 an hour. The reason behind hiring undocumented people is so you don't need to pay them the minimum wage, which you seem to have missed.
Anyway, California's agriculture industry would be dead without illegal immigrants. More than a million of them work on the farms and vineyards for a pittance.
They are the new slave labour.
I wonder how many Trump supporters who want them gone would take a job picking avocados in 40 degrees for $10 an hour.