Burning Man is supposed to arrive and disappear like the desert breeze. Near the end of every summer, attendees of the multiday mega-festival venture to the Nevada wilderness. Their motto: “Leave no trace.” This year, thousands got stuck in the mud instead after about a half an inch of rain hit what is normally the driest state in the nation. Instead of leaving no trace, many self-described “burners” abandoned bicycles and vehicles on the drenched, muddy Black Rock Desert. Once an underground carnival for free spirits, Burning Man today is famous as a party spot for Hollywood stars, Silicon Valley...