Cal. Sts. & Hy. Code § 1686
The Legislature hereby finds that the improvement and maintenance of all city streets is of general county interest. The board of supervisors of any county may, by resolution adopted by a four-fifths vote of its members, determine that county aid shall be extended for the improvement or maintenance of streets within a city or extending along or across the boundary of a city.
Such resolution shall specify the general nature of the improvement and maintenance proposed, the nature of the aid to be furnished by the county, and any funds from which the aid is to be paid. Such resolution need not specify the streets to be improved or maintained within such city but may in general terms specify the general character of the work proposed and require such reports and accounting of the expenditure of such aid funds as it may find to be necessary and convenient. The provisions of this section shall be deemed as an alternative procedure to that otherwise specified in this article.
Ca. Sts. and High. Code § 1686