There are just a couple rules. Chief among them: “Don’t be a dick.”

On June 28, around 4,000 drivers and crew will head out (some leave from shared starting points, like the Portland Expo Center or Wilsonville’s World of Speed Museum) for a 500-mile road rally through some of Oregon’s dustiest, dirtiest country roads. The twist: they have to get to the finish line, a giant bonfire party in rural Chemult, in a beater costing no more than $500. That price cap results in a truly bizarre procession of cars, from trusty Civics to crudely spray-painted Cadillacs to rusty boats hand-welded onto 4Runner chasses.

This is the Gambler 500, an annual mobile party for anyone with a few hundos or an old Buick growing moss in the driveway. Founder Tate Morgan (by day, a Portland business consultant) started the rally in 2014 with a group of friends looking for a cheap challenge. In 2016, a phone-shot video of their off-roading shenanigans went viral. Now, the Gambler 500 has sister events from Tennessee to Canada to Iceland.

“We weren’t trying to launch what is now the largest rally in the world,” says Morgan. “Going from 13 cars to 850 cars in year four—that was unexpected.”

Morgan, who says he visited nearly every national park growing up as the son of a US Geological Survey hydrologist, is well aware of the environmental cost of unleashing so many gas-guzzling junkers on Oregon’s backcountry. So, the event doubles as a garbage cleanup. So far, he estimates, Gamblers have picked up 180 cubic yards of trash en route to rally endpoints.

“It makes sure that we’re getting the right people,” Morgan says. “This is not a wild, crazy, blow-up-a-car rally. This is a fun outdoor adventure where we’re leaving trails better than we found them.”