California Code, Probate Code - PROB § 17005

(a) The proper county for commencement of a proceeding pursuant to this division is either of the following:

(b) If a living trust has no trustee, the proper county for commencement of a proceeding for appointing a trustee is the county where the trust property, or some portion of the trust property, is located.

(c) Except as otherwise provided in subdivisions (a) and (b), the proper county for commencement of a proceeding pursuant to this division is determined by the rules applicable to civil actions generally.