BLACK ROCK DESERT, Nev. (AP) — Partygoers stranded for days at a counterculture festival by a late summer storm were allowed to start leaving Monday afternoon after muddy roads dried up enough for them to begin their exodus from the northern Nevada desert. An unusual late-summer storm turned the week-long Burning Man fest into a sloppy mess, with tens of thousands stuck in foot-deep mud and with no working toilets. The gathering in the Black Rock Desert north of Reno attracts nearly 80,000 artists, musicians and activists for a mix of wilderness camping and avant-garde performances. More a half-inch of rain fell at the festival site on Friday, the National Weather Service in Reno said. At least one death has been reported. But festival organizers say it wasn’t weather-related.