Starting Jan 1, it's a mandatory impoundment of 30 days if you are arrested for exhibition of speed.
http://www.leginfo.ca.gov/pub/bill/sen/sb_1451-1500/sb_1489_bill_20020821_enrolled.html
http://www.leginfo.ca.gov/pub/bill/sen/sb_1451-1500/sb_1489_bill_20020821_enrolled.html