Is ignorance of the law a defense in a sexual assault case?

"In determining whether a defendant's mistaken belief disproves criminal intent, the courts have drawn a distinction between mistakes of fact and mistakes of law. [Citation.] While a mistake of fact usually is a defense, a mistake of law usually is not. It is commonly said that ignorance of the law is no excuse. [Citation.] '[I]n the absence of specific language to the contrary, ignorance of a law is not a defense to a charge of its violation.' [Citation.] 'If the act itself is punishable when knowingly done, it is immaterial that the defendant thought it was lawful.' [Citation.] As an illustration: a defendant's ignorance of a girl's age may be a defense to statutory rape, but a defendant's ignorance of the law prohibiting sex with underage girls is no defense." (People v. Meneses (2008) 165 Cal.App.4th 1648, 1661-1662.)