This is a good article. http://www.sfgate.com/news/article/Agricultural-technology-use-growing-in-California-4796028.php#page-1
With agricultural prices high and farmers increasingly comfortable with technology, it would be great for the Valley economy to see some of these profits invested to modernize the agriculture industry and help farmers adjust to a changing labor market. In addition to these immigration and demographic patterns, farmers are adjusting to increasing responsibility for their employees healthcare costs due to the implementation of Obamacare, and California appears poised to raise the minimum wage.
For economic development in the Valley, the focus needs to shift from counting the number of agriculture jobs to a focus on raising the quality, pay and skill requirements for Valley agriculture jobs. It would be useful to see policy to support this adjustment. Philip Martin's ideas for modifying the Ag jobs immigration proposal is an example of a policy approach that could support this transition (link).