stoked_dude said it on the SCS forum here http://forum.scssoft.com/viewtopic.php? ... &start=620 (about half way down the page)

They inspect inbound traffic for produce, and invasive vegetation. Almost every major route into Cali has them, and they are the only state that has them. You can read more about them here https://www.cdfa.ca.gov/plant/pe/Exteri ... rders.html