What is sufficient to establish probable cause when a witness gives evidence of illegal activity?

"An informant's description of illegal activity is sufficient to establish probable cause if the totality of the circumstances indicate that the tip is reliable." United States v. Elliot, 893 F.2d 220, 223 (9th Cir.), amended on other grounds, 904 F.2d 25, cert. denied, 498 U.S. 904 (1990). " 'A detailed eye-witness report of a crime is self-corroborating; it supplies its own indicia of reliability.' " Id. ( quoting United States v. Estrada, 733 F.2d 683, 686 (9th Cir.), cert. denied, 469 U.S. 850 (1984), and cert. denied, 469 U.S. 861 (1984)).