California Code, Insurance Code - INS § 11840

The insurance contracts or policies of the State Compensation Insurance Fund may be either limited or unlimited.  The insurance contracts or policies may be issued for like periods as are allowed by law to other workers' compensation insurers or, in the form of stamps or tickets or otherwise, for one month, for any number of months less than one year, for one day, for any number of days less than one month or during the performance of any particular work, job or contract.  The rates charged shall be proportionately greater for a shorter than for a longer period and a minimum premium charge shall be fixed in accordance with a reasonable rate for insuring one person for one day.