CA Gov't Code Section 56388

If any proposal involves a district which is, or as a result of a proposed change of organization or reorganization would be, located in more than one county, exclusive jurisdiction for that proposal over the matters authorized and required by this part may be vested in the commission of a county, other than the principal county, in which territory of the district is located or is proposed to be located if all of the following occur:

(a)

The commission of the principal county agrees to having the exclusive jurisdiction vested in the commission of another county.

(b)

The commission of the principal county designates the commission of another county which shall assume exclusive jurisdiction.

(c)

The commission of the county so designated agrees to assume exclusive jurisdiction.