Well, I'm guessing that some genius climbers who were moving slow got benighted and decided to stay warm with a fire. Someone said they saw a fire up there on Monday night. Anyway, they started a fire basically at the point that the walkoff for the Royal Arches route meets the rim. Bad climber! No chalk!
I first noticed the smoke while out for a lunchtime walk to meet my sweetheart and then the helicopters came around 2:00pm. I didn't see any flames until someone roused us around 7:30pm to go have a look. I got some pretty decent pictures of the fire on top of Royal Arches, but there were a couple of times when it really flared up and i was not ready with the camera, so I missed those. I also missed the best of the firefalls. By 8:00pm there was a substantial fire on the ledges that were below tree line. We could see them clearly through the trees, but couldn't really get pictures and I didn't want to cross the valley to get a better look, but I think the Royal Arches climbing route was on fire. That's unconfirmed, just my guess as looking at it from Stoneman's Meadow. Good job dude!