In most cases, a California DUI arrest results in two separate processes: criminal prosecution in a California court and license suspension proceedings with the California Department of Motor Vehicles (DMV).
This assumes, though, the person arrested has a California drivers license. An out-of-state driver can face a third process if the state that issued her license is a member of the Interstate Drivers License Compact.
The Interstate Drivers License Compact is an agreement among 45 states to share information regarding driving violations committed by out-of-state drivers within their borders. California joined in 1963.
The theory behind the Interstate Drivers License Compact is "one driver, one license, one record." In practice, this means the California DMV will notify the "member state" that issued your license that you were arrested here for DUI∗. Depending on its DUI laws, consequences to your driving privileges may follow you home, including suspension.
People should also understand this process applies only to driving privileges. You cannot be prosecuted in one state for a DUI arrest that occurred in another.
Ultimately, the best way to deal with potential "home state" consequences is to defeat the California DUI charge that may trigger them. That means consulting with an experienced attorney who can represent you in court, as well as before the California DMV.
∗The non-member states are Wisconsin, Tennessee, Georgia, Massachusetts, and Michigan.