Any person desiring to make any excavation for any purpose in or across any road outside any incorporated city or town, not in the State highway system, shall make and file with the county supervisor an application in writing for permission to make such excavation. Such application shall state fully the nature, purpose, extent and depth of the proposed excavation and shall contain such further information as may be required by the supervisor. Before such permission shall be granted the applicant shall execute and deposit in the office of the supervisor a good and sufficient bond of indemnity, or cash, in such sum as may be required to repair the road and restore it to as good condition as to foundation and surface as it was before being excavated. When such excavation is to be made by a solvent public utility, such bond may be executed by the utility without additional surety.