Part 4. Mining Industries of California Labor Code >> Division 5. >> Part 4.

In all mines operated in the State where a depth of more than five hundred feet underground has been reached, a telephone system shall be established, equipped and maintained by the owners or lessees of the mine with stations at each working level below the depth aforesaid, communicating with a station on the surface of the mine.
The failure or refusal of any owner or lessee to install or maintain such telephone system is a misdemeanor.