In most DUI arrests your license to drive is immediately confiscated (unless you have an out-of-state license) and you are given a pink sheet of paper.
This paper serves as a formal notice of an immediate suspension, a temporary license good for 30 days and a brief explanation of the laws and procedures involved. IMPORTANT: you only have 10 days from your arrest to call the Department of Motor Vehicles to schedule a hearing to contest the suspension. On the 11th calendar day the DMV will refuse to provide a hearing and the suspension (at least 4 months) will automatically take effect in 30 days. Although, a late hearing request may be granted for "good cause".
The basis for this suspension is California's "implied consent" laws. These laws essentially say that any person driving in California is "presumed" to imply consent to chemical testing if he or she is suspected of drunk driving. ( see Implied Consent Tab)
It is always recommended that you, or the attorney you hire, immediately contact the DMV to request a hearing. There is a good chance of having the suspension thrown out; the worst thing that can happen is that the same suspension will simply take effect, but later than 30 days.
The California DMV has a useful overview of DUI and DMV actions. www.dmv.ca.gov/portal/dmv/detail/video/lets_drive/ca_dl