WORKING TO ASSIST DELAYED PASSENGERS. >>> AND THE MASS EXODUS FROM BURNING MAN IS SLOWLY MOVING FORWARD AFTER RAIN AND MUD TRAPPED MORE THAN 70,000 FESTIVAL GOERS FOR DAYS. BUT NOW THERE IS NEW CONCERN OVER WHAT THEY'RE LEAVING BEHIND. OUR LIZ KREUTZ IS THERE. >> Reporter: AT BURNING MAN'S BLACKROCK CITY, DAYS TRAPPED IN MESSY SLUDGE HAS NOW TURNED TO HOURS STUCK IN GRIDLOCK TRAFFIC. >> IT WAS A GREAT BURN UNTIL IT RAINED. >> Reporter: TONIGHT THE SLOW CRAWL OUT OF THE REMOTE DESERT FESTIVAL STRETCHING FOR MILES. TENS OF THOUSANDS STILL TRYING TO GET OUT. THIS IS WHERE FESTIVAL GOERS FINALLY REACH A PAVED ROAD. BUT GETTING HERE IS A LESSON IN PATIENCE. FOR SOME, THE SIX-MILE TRIP OUT TAKING AS LONG AS NINE HOURS. AND NOW QUESTIONS ARE MOUNTING OVER THE CHAOTIC MESS LEFT BEHIND. THE I PERSHING COUNTY SHERIFF SLAMMING THE CONDUCT OF FESTIVAL GOERS, TELLING "THE SAN FRANCISCO CHRONICLE" SOME ABANDONED THEIR PROPERTY AND VEHICLES, LEAVING TRASH ACROSS SEVERAL MILES AS THEY SCRAMBLED TO ESCAPE THE STORM. >> THERE HAVE BEEN PEOPLE THAT HAVE LEFT THINGS. I THINK A LOT OF PEOPLE HAD A VERY FEAR-BASED REACTION. >> Reporter: ORGANIZERS HAVE NOT RESPONDED TO NBC'S REQUEST FOR COMMENT ABOUT THE AFTERMATH, BUT VETERAN FESTIVAL GOERS LIKE TERRY GAULT, WHO IS STAYING BEHIND TO CLEAN UP, ARE FRUSTRATED. >> WE KNOW THAT PEOPLE ABANDONED THEIR CAMPS. SO IT'S NOT SURPRISING TO HEAR THAT THERE WAS TRASH LEFT BEHIND. >> WHAT'S YOUR MESSAGE TO PEOPLE WHO LEAVE THINGS BEHIND? >> WELL, ONE OF THE TEN PRINCIPLES IS LEAVE NO TRACE. FOR SO THOSE PEOPLE WHO LEFT TRASH BEHIND, THOSE AREN'T REAL BURNERS. THEY PROBABLY SHOULDN'T BE OUT HERE ANY WAY. >> Reporter: THIS ALL COMES AS AUTHORITIES CONTINUE TO INVESTIGATE THE DEATH OF A MAN AT THE HEIGHT OF THE STORM. AUTHORITIES SAY THERE IS NO INDICATION IT WAS WEATHER-RELATED, BUT THAT CONDITIONS MAY HAVE SLOWED THEIR RESPONSE. WHILE MOST TODAY ARE GOING OUT BY CAR, SOME FINDING WAYS TO AVOID THE CONGESTION. >> WITH THE BIKE IT WAS JUST MINUTES. >> Reporter: TONIGHT WITH HALF THE FESTIVAL STILL INSIDE, THE FAMOUS BURNING MAN IS GONE, BUT A MASSIVE CLEANUP EFFORT STILL LIES AHEAD.