California Code, Labor Code - LAB § 2350

Every factory, workshop, mercantile or other establishment in which one or more persons are employed, shall be kept clean and free from the effluvia arising from any drain or other nuisance, and shall be provided, within reasonable access, with a sufficient number of toilet facilities for the use of the employees.  When there are five or more employees who are not all of the same gender, a sufficient number of separate toilet facilities shall be provided for the use of each sex, which shall be plainly so designated.