California Code, Health and Safety Code - HSC § 13052.5

The governing board of any county fire protection district may contract with any city contiguous to the district for the furnishing of fire protection to the district by such city, and the legislative body of any city may contract for the furnishing of fire protection to the district in such manner and to such extent as the legislative body may deem advisable.

All of the privileges and immunities from liability which surround the activities of any city fire fighting force or department when performing its functions within the territorial limits of the city shall apply to the activities of any city fire fighting force or department while furnishing fire protection outside the city under any contract with a county fire protection district pursuant to this section.