Where there is no written agreement between the County and the private property owner there shall be a legal right by maintenance of roads by the County. This is called and Implied Dedication through maintenance and expenditure of public funds. See California Codes Civil Code Section 1006-1009 below or visit website:
https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=CIV§ionNum=1009.
CALIFORNIA CODES CIVIL CODE SECTION 1006-1009
1009 (d) Where a governmental entity is using private lands by an expenditure of public funds on visible improvements on or across such lands or on the cleaning or maintenance related to the public use of such lands in such a manner so that the owner knows or should know that the public is making such use of his land, such use, including any public use reasonably related to the purposes of such improvement, in the absence of either express permission by the owner to continue such use or the taking by the owner of reasonable steps to enjoin, remove or prohibit such use, shall after five years ripen to confer upon the governmental entity a vested right to continue such use.