Cal. Water Code § 74031

A district may be organized upon petition by the qualified electors in an area comprising the whole or a part or parts of one or more watersheds of any stream or streams of water or unnavigable river or rivers, or territory adjacent to such watershed or watersheds, or deriving such area’s water supply, in whole or in part, from such stream or streams, or river or rivers, or the subterranean supply of waters therefrom, for the conservation of the waters of such stream or streams or unnavigable river or rivers.