CAN I BRING HAY INTO CALIFORNIA?
In general, there are not specific restrictions on bringing hay into California; however, it must be free from noxious weeds and insect pests and is subject to inspection upon arrival at our border stations. If bringing hay, be sure it is loaded so the outer surface of the bales can be easily seen. Most hay passes inspection, but occasionally pests are found and the shipment is rejected. In this event, you may need to return the hay out-of-state if it cannot be easily disposed of at the station.
This is copy and pasted from: www.cdfa.ca.gov/plant/pe/ExteriorExclusion/borders_faq.html you can go to either of these links for more information http://www.cdfa.ca.gov/