California Code, Fish and Game Code - FGC § 2250

It is unlawful to import or transport any live muskrat (genus Ondatra) into, or possess any live muskrat in, California except under permit issued by the department pursuant to Section 2118, or as otherwise provided by law. A county agricultural commissioner, fish and game deputy, or state plant quarantine officer may enter upon lands or waters west of the crest of the Cascade-Sierra Nevada mountain system, and west and south of the Tehachapi, Liebre, San Gabriel, San Bernardino, San Jacinto, Cuyamaca, and connected mountains south to the international boundary, or in any watershed tributary to, or draining into, the Pacific Ocean to remove or destroy the muskrats.