California Code, Insurance Code - INS § 11580.6

Where a policy of liability insurance covering the ownership, maintenance, or use of a motor vehicle or aircraft contains a provision indicating that coverage is extended to accidents, occurrences, and loss arising in Mexico, the policy shall contain an additional provision, either on the face of the policy or by an endorsement attached thereto stating as follows:

Unless you have automobile or aircraft insurance written by a Mexican insurance company, you may spend many hours or days in jail, if you have an accident in Mexico. Insurance coverage should be secured from a company licensed under the laws of Mexico to write such insurance in order to avoid complications and some other penalties possible under the laws of Mexico, including the possible impoundment of your automobile or aircraft.