Usually done as a finish to Poison Spider
, this trail drops 1,000' in a mile, with huge exposure next to a 1,300 foot cliff. People have fallen and died here. It's incredibly unique and scenic, but riding it should only be attempted by experts, and intermediates with a great attitude should be willing to walk most of it.
Starting from the end of the Poison Spider
trail, the Portal Trail hugs the rim with a nice easy downhill grade and smooth, easy surface at first. This doesn't last long and it's time to wake up when you see the "Dismount Here" sign from the BLM. They mean it. Unless you've done this section before, really know what you're doing, and are prepared to die to do it again, go ahead and dismount. It's not that the moves are all that impossible, but the consequences are all that bad, and several boulders want to push you right off the trail and over the cliff.
Continue for about half a mile right on the edge of the rim. Several sections are rideable by intermediate riders, but most people will dismount for many short sections. Enjoy the amazing views of Moab and the La Sal mountains beyond.
The trail takes a sharp right and is now directly above the Colorado River. It is no longer right on the edge of the cliff, so that danger is mostly past, but now the descent begins in earnest: the next mile loses 1,000' over many drops, ledges, and pinches. Most people will feel more comfortable walking many sections, though about half might be rideable by intermediates.
The trail finishes along the highway, where you'll either ride back to town or to your car at the Poison Spider