California Code, Streets and Highways Code - SHC § 105

The department may construct and maintain stock trails approximately paralleling any State highway and may retain and maintain for stock trails the right of way of any State highway which is superseded by relocation.

The department may likewise designate as a stock trail any highway which the State has relinquished to a county and which approximately parallels any State highway.  Where such a highway has been so designated as a stock trail, it thereafter may not be abandoned or vacated without the consent in writing of the department filed with the board of supervisors.

The department shall post notices upon such stock trails, and upon each highway at the entrances of such trails, directing all persons to drive all untethered stock thereon.

Any person who drives any untethered stock upon any State highway between the entrances of such a stock trail is guilty of a misdemeanor, and, in addition thereto, is liable for all damage thereby done to said highway.