Above Abyss can be done as a longer version of the Slickrock trail, bypassing one mile of the main trail that includes the main loop fork. Or, you can do Above Abyss as your destination ride, turning back once you hit Slickrock. If you do the practice loop then Above Abyss before heading back on the main route, it makes a nice lariat ride of 8.1 miles and 2000 vertical feet of climbing.

At this time (2019), the hardest thing about riding Above Abyss is finding it. So pay attention to the following instructions!
On the outgoing Slickrock trail, you'll get briefly entangled with the Hell's Revenge 4x4 trail at mile 1.7. As you get away from the 4x4 route, you'll do 3 steep climbs. At the ridge after the third climb, you'll see the trail turn 90 degrees to the right and drop very steeply down and across the 4x4 path. But don't turn downhill!

You're now almost exactly one mile past the second practice loop fork, or mile 1.8 from the trailhead if you came via the main trail. Ignore the descending trail to your right and instead pedal straight ahead on top of the fin of rock. After about 30 feet, you'll notice the first paint dot on the rock. Follow the dots. In about 1/10th mile, you'll hit the first little trail sign confirming that you're on the trail.

The trail is fairly easy to follow once you find it. If you lose the paint dots while riding fast and eyeballing the scenery, backtrack a bit to see where you lost the riding line.
At mile 0.9 of Above Abyss, the trail gets close to the Hell's Revenge 4x4 route. Keep to the right at anything that looks like a connecting route. I didn't find anything confusing here.

As mentioned, the riding is significantly easier than many areas of the Slickrock trail. Climbs are short, with nothing near as steep as the slopes you struggled up before entering Above Abyss. There are a couple of wheel-trap dips as you first start the trail, but otherwise it's a very non-tricky ride.

You'll have frequent views into the canyon and of the La Sals. At mile 1.4, there's a nice viewpoint as the trail turns from northbound to westbound on the edge of the canyon. It's worth a stop here.

At mile 1.6 Above Abyss crosses the Hell's Revenge 4x4 path. As you hit the blackened 4x4 route, keep straight and head onto the rock on the other side. (Have faith. You won't see any sign of the continuing trail until you've gone about 50 feet.)

Above Abyss will now skirt the head of Icebox Canyon at around mile 1.9. The views here are awesome. At the far side of the canyon, watch for a painted trail fork on the rock. To the right is a 200-foot spur to overlook the canyon. Left is the way out.

About 100 yards after the trail fork for the overlook spur, there's a second trail fork painted onto the rock. (The circle designates a fork, with the dots outside the circle showing the possible riding directions.) Straight and right is a short 1/10th mile connector to the main Slickrock trail. Use this if you're planning to finish the main Slickrock loop counterclockwise.

The left fork goes 0.2 miles to the Slickrock trail, and would be your preferred path if you're heading back to the trailhead. This route is also prettier and more fun. As you reach the main Slickrock trail, fork left. After one mile, you'll hit the main loop fork. Go left to head for parking.
If you're riding the main loop clockwise, finding the Icebox Canyon connector is a bit harder because of a lack of landmarks. Starting about 1/2 mile after Shrimp Rock, watch carefully on your left for paint spots on the rock. You have two chances to find a trail. Or use GPS (tracks downloadable below).

Bottom Line!
Nice trail. Not too difficult compared to Slickrock overall. Makes a nice alternative ride if you're bored with the main trail, or extra miles if you're one of those superhumans who aren't challenged enough by the main ride.