What is the test for establishing a statute of limitations for sexual assault?

" 'The purpose of a statute of limitations is to limit exposure to criminal prosecution to a certain fixed period of time following the occurrence of those acts the legislature has decided to punish by criminal sanctions. Such a limitation is designed to protect individuals from having to defend themselves against charges when the basic facts may have become obscured by the passage of time and to minimize the danger of official [214 Cal.App.3d 1493] punishment because of acts in the far-distant past. Such a time limit may also have the salutary effect of encouraging law enforcement officials promptly to investigate suspected criminal activity.' " (United States v. Marion (1971) 404 U.S. 307, 323, 92 S.Ct. 455, 465, 30 L.Ed.2d 468 citing Toussie v. United States (1970) 397 U.S. 112, 114-115, 90 S.Ct. 858, 860, 25 L.Ed.2d 156.)