Section 7500 Of Part 4. Mining Industries From California Labor Code >> Division 5. >> Part 4.
7500
. 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.