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.
Cal. Lab. Code § 7500
Underground Telephones
Enacted by Stats. 1937, Ch. 90.
Official source: California Legislative Information. Reproduced from public-domain California statutes; confirm against the official source for the current text. Not legal advice.