Cal. Rev. & Tax. Code § 40081

If any person fails to make a return, the board shall make an estimate of the amount of kilowatt-hours sold for consumption by the person, or, as the case may be, of the amount of kilowatt-hours purchased by the person, the consumption of which in this state is subject to the surcharge. The estimate shall be made for the period or periods in respect to which the person failed to make a return and shall be based upon any information which is in the board’s possession or may come into its possession. Upon the basis of this estimate the board shall compute and determine the amount required to be paid to the state, adding to the sum thus arrived at a penalty equal to 10 percent thereof. One or more determinations may be made for one or for more than one period.