DMV on line에 들어가보니까 아래와 같이 써있던데요.
제가 해석이 좀 서툴러서요.
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International Driving Permit

International Driving Permits 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. Citations issued to a person in California who has an IDP, but does not have a California driver license will be placed on the Department of Motor Vehicle database. The IDP is also called an International Driver License, International License, etc. For more information about travel and driver licensing requirements outside of the US, visit the US State Department Road Safety Overseas website at: http://travel.state.gov/road_safety.html