Cal. Code Regs. tit. 8, § 7050 – (9-107). Stopes.

(a) Floors shall be provided in every stope where needed for the safety of employees.
(b) In stopes timbered with square sets those portions of the working floors that are in use shall be closely and securely lagged.
(c) An adequate work floor shall be provided in narrow stopes that are too steep to permit safe footing.