Officials collected several pounds of marijuana and pot paraphernalia from five buses, carrying some 250 students.
The Bay Area teenagers were traveling to a ski resort in Utah.
Police said they made a pit stop in Elko, Nev. when a convenience store clerk became suspicious that they'd been smoking marijuana in the parking lot.
"The Maverick store people called us so our officers went with our K-9 units. The sheriff's department K-9 was there as well to assist us. The drug dogs hit on all five buses," said Elko Police Chief Don Zumwalt.
The teenagers got off with just a warning, mainly because there was a lack of jail space for such a large group in the small Nevada town. The juvenile detention facility in Elko has 20 beds.
Zumwalt gave the teenagers a lecture about responsibility before sending them on their way.
Zumwalt said he was trying to contact officials with the tour operator, Summer Winter Action Tours, based in Costa Mesa, Calif. A website touts the trip, dubbed El Nino 2011, as a gathering of high school students from 67 schools in Los Angeles, Orange County, Temecula and Arizona, 27 schools in the San Diego area, and 40 schools in Northern California.
KRNV-TV in Reno said a company official called it almost impossible to control what people bring onto the bus.
The Associated Press contributed to this report.