CA Prob Code Section 4523

The proper county for commencement of a proceeding under this division shall be determined in the following order of priority:

(a)

The county in which the principal resides.

(b)

The county in which the attorney-in-fact resides.

(c)

A county in which property subject to the power of attorney is located.

(d)

Any other county that is in the principal’s best interest.