Cal. Health & Safety Code § 13054

Where the personnel, equipment, and facilities of any county are utilized in the extinguishment or control of any fire outside its boundaries, the county furnishing its personnel, equipment, and facilities shall be reimbursed by the county in which the fire occurs in an amount in accordance with a predetermined schedule of repayments agreed upon by the boards of supervisors of the counties, or between the board of supervisors of the county and the Department of Forestry and Fire Protection or the United States Forest Service, as the case may be.