http://www.txdot.gov/business/motor_.../temporary.htm
When we bought our trailer in Oregon the dealer had a temporary permit ready for us...perhaps this is what you can get from Texas.
You have (I think) 30 days to register in CA, and you will have to pay sales tax and the registration fee. TM's are not like smaller tent trailers that get a PTI (unless you're lucky & the DMV you go to gives you one, it's happened before) so you have to pay an annual licensing fee.
Upon further reading, you may be able to get one from California before you leave...
http://www.dmv.ca.gov/pubs/reg_hdbk_pdf/ch25.pdf
Their rules are so complex, I'd call them.