Popper, 39, was arrested Tuesday afternoon on Interstate 90 near the Spokane/Lincoln county line, the Washington State Patrol said.
Inside the black Mercedes SUV, officers found a cache of weapons and a small amount of marijuana, the Patrol said. A police dog searched the vehicle, finding numerous hidden compartments containing four rifles, nine handguns and a switchblade knife. Authorities also found a Taser and night vision goggles. The vehicle was seized.
Popper, who lives in Snohomish, Wash., is the owner of the vehicle, which was being driven by Brian Gourgeois, 34, of Austin, Texas, said state patrol Trooper Jeff Sevigney. The vehicle also had flashing emergency headlights, a siren and a public address system, the Patrol said.
"Popper indicated to troopers that he had installed these items in his vehicle because (in the event of a natural disaster) he didn't want to be left behind," the Patrol said in a news release. He also told officers he collected weapons, the Patrol said.
The two men were booked administratively into the Adams County jail and released on their own recognizance. Authorities plan to charge them with possession of a controlled substance and possession of drug paraphernalia. Gourgeois will also face a charge of reckless driving, the Patrol said.
Popper did not immediately return an e-mail seeking comment Wednesday night.
Popper achieved fame as a harmonica player and frontman for Blues Traveler. The band won a Grammy award in 1996 for the song "Run-around," which Popper composed.
Popper recently formed a group called The John Popper Project with DJ Logic, which released an album in 2006 and is scheduled to go on the road later this month.