California Code, Evidence Code - EVID § 604

The effect of a presumption affecting the burden of producing evidence is to require the trier of fact to assume the existence of the presumed fact unless and until evidence is introduced which would support a finding of its nonexistence, in which case the trier of fact shall determine the existence or nonexistence of the presumed fact from the evidence and without regard to the presumption.  Nothing in this section shall be construed to prevent the drawing of any inference that may be appropriate.