WASHINGTON -- Thousands of revelers are converging this week in Nevada's Black Rock Desert for the Burning Man Festival, where they'll camp, create and observe art and music, and where, perhaps, they'll encounter an undercover FBI agent.

Documents obtained by the journalist Inkoo Kang, and posted to the website MuckRock, reveal that the event has been under FBI surveillance since at least 2010. That is when the agency concluded that Burning Man is "considered a cultural and artisan event, which promote (sic) free expression by the participants."

In one document from 2010 agents conclude that the "greatest known threat in this event is crowd control issues and use of illegal drugs," but in a heavily-redacted report produced less than a month later, the agency's Special Events Management unit seems to note that the event is used to practice intelligence collection and anti-terrorism security.

Burning Man 2015
Burning Man 2015 takes place August 30 – September 7, 2015 in the Black Rock Desert of Nevada. Participants join in the effort to co-create Black Rock City, a temporary metropolis dedicated to art and community.