California Code, Public Utilities Code - PUC § 7630

Upon hearing the commission shall determine whether or not any fence or fences are necessary to protect cattle, horses, mules, or any other domestic animals being ranged or grazed upon the land designated in the application, from being maimed, or killed by the operation or management of engines, cars, or other rolling stock upon the railroad, and shall order that a fence or fences be constructed and maintained by the railroad corporation at such places along the railroad adjacent to the lands designated in the petition as the commission determines. The commission may fix the time within which the fence or fences shall be constructed and may designate the places for necessary openings and gates therein and crossings and cattle guards in connection therewith.

The commission may modify or revoke any such order when it determines that the necessity for any such fence has ceased to exist.