The officers repeatedly found human footprints in the sand that indicated that groups of 8 to 20 persons had walked north from the Mexican border to Arizona State Route 86.

[4] The Supreme Court unanimously reversed the Ninth Circuit, ruling that the Border Patrol had reasonable suspicion to stop Cortez's vehicle.

Chief Justice Burger emphasized that reasonable suspicion must be based on the "totality of the circumstances," and does not depend on "hard certainties, but ...

"[6] Based on their familiarity with the area and on their two-month period of observation, the officers concluded that "Chevron" had a regular pattern of operations.

"[6] In a concurrence, Justice Stewart highlighted the facts of the case, writing, "this nocturnal round trip into desolate desert terrain" was "in any event ... puzzling," but "coming when and as it did, surely the most likely explanation for it was that Chevron was again shepherding aliens.