Cal. Health and Safety Code § 11838

(a) The Legislature encourages all counties to utilize the procedure described in this chapter, but recognizes that it is not feasible for every county to establish its own programs. Accordingly, two or more counties may jointly establish programs pursuant to Section 11796 of this code or Article 1 (commencing with Section 6500) of Chapter 5 of Division 7 of Title 1 of the Government Code or may furnish by contract the program services to residents of another county pursuant to Section 11796 of this code. The board of supervisors of the county in which the program is located shall be responsible for assuring the integrity of the program as required pursuant to subdivision (a) of Section 11837.6. (b) For the purpose of determining a person’s eligibility to participate in an approved program where the person’s county of residence establishes a program with another county or contracts for services pursuant to subdivision (a), the following eligibility requirements shall apply: (1) Where two or more counties jointly establish a program pursuant to Section 11796 of this code or Article 1 (commencing with Section 6500) of Chapter 5 of Division 7 of Title 1 of the Government Code, subdivision (b) of Section 11838.2 shall apply. (2) Where a county contracts for program services from another county, only those residents alleged to have committed a violation of Section 23152 or 23153 of the Vehicle Code on or after the date their county of residence executes a contract pursuant to subdivision (a) to provide program services to their residents shall be eligible to participate in such approved program pursuant to Section 11837.2. Counties which contract for services pursuant to subdivision (a) of this section shall notify the department not later than 14 days following such action.