Cal. Civ. Proc. Code § 198.5

If sessions of the superior court are held in a location other than the county seat, the names for master jury lists and qualified jury lists to serve in a session may be selected from the area in which the session is held, pursuant to a local superior court rule that divides the county in a manner that provides all qualified persons in the county an equal opportunity to be considered for jury service. Nothing in this section precludes the court, in its discretion, from ordering a countywide venire in the interest of justice.