Veh. Code, § 21350

The Department of Transportation shall place and maintain, or cause to be placed and maintained, with respect to highways under its jurisdiction, appropriate signs, signals, and other traffic control devices as required hereunder, and may place and maintain, or cause to be placed and maintained, such appropriate signs, signals, or other traffic control devices as may be authorized hereunder, or as may be necessary properly to indicate and to carry out the provisions of this code, or to warn or guide traffic upon the highways. The Department of Transportation may, with the consent of the local authorities, also place and maintain, or cause to be placed and maintained, in or along city streets and county roads, appropriate signs, signals, and other traffic control devices, or may perform, or cause to be performed, such other work on city streets and county roads, as may be necessary or desirable to control, or direct traffic, or to facilitate traffic flow, to or from or on state highways.