What is the test for establishing probable cause when a witness reports illegal activity?

Probable cause exists where "there is a fair probability that contraband or evidence of a crime will be found in a particular place." Illinois v. Gates, 462 U.S. 213, 238 (1983). An informant's description of illegal activity can establish probable cause if the totality of the circumstances indicate that the "tip is reliable." United States v. Elliott, 893 F.2d 220, 223 (9th Cir.1990) (citing Gates, 462 U.S. at 230). "A detailed eye-witness report of a crime is self-corroborating; it supplies its own indicia of reliability." Id. (citations omitted).