The State of California does not recognize an International Driving Permit (IDP) as a valid driver license. California does recognize a valid driver license that is issued by a foreign jurisdiction (country, state, territory) of which the license holder is a resident. The IDP is only a translation of information contained on a person's foreign driver license and is not required to operate a motor vehicle in California.

http://www.dmv.ca.gov/dl/dl_info.htm#international