What is the test for a motion to suppress a marijuana possession conviction?

Following the district court's denial of their motions to suppress, Mayer, Ketaner, and Gomes pleaded guilty to possession with intent to distribute marijuana. They now appeal their convictions, arguing, inter alia, that the government lacked sufficient probable cause to justify the warrantless searches of their automobiles. We review de novo a district court's finding of probable cause and its determination of the legality of warrantless searches, United States v. Linn, 862 F.2d 735, 739-40 (9th Cir.1988), and we affirm.