In California, employees and employers may adopt an alternative workweek schedule or AWS.   An AWS is any regularly scheduled workweek requiring an employee to work more than eight hours in a 24-hour period.

If employees who are under a AWS receive few than the number of scheduled hours then a short shift has occurred.  For short shifts, employees are paid overtime for hours worked in excess of 8 and double time for hours in excess of 12.  From

For all Orders except Order 16, if the employer requires an employee to work fewer hours than those that are regularly scheduled, the employer must pay the employee overtime at the rate of one and one-half times the employee’s regular rate of pay for all hours worked in excess of eight hoursand, of course, double the employee’s regular rate of pay for all hours worked in excess of 12 hours for the day the employee is required to work the reduced hours.

For Order 16 only, an employee who works longer than eight hours but no more than 10 hours in a workday pursuant to an alternative workweek schedule, must be paid an overtime rate of not less than one and one-half times his or her regular rate of pay for any work in excess of the regularly scheduled hours established by the agreement.