California Code, Government Code - GOV § 8623

During a state of war emergency, any person holding a license, certificate, or other permit issued by any state evidencing the meeting of the qualifications of such state for professional, mechanical, or other skills, may render aid involving such skill to meet the emergency as fully as if such license, certificate, or other permit had been issued in this state if a substantially similar license, certificate, or other permit is issued in this state to applicants possessing the same professional, mechanical, or other skills.