The Rockstacker Trail is a highly technical singletrack route that connects the Pothole Arch Trail to the Jackson Singletrack at the top of Amasa Back . It's only 1.7 miles long but involves a lot of work both uphill and downhill. There are some very dangerous spots. Only true experts should attempt this ride.
The ride description below is the way I rode it, but my honest suggestion is that you skip Jackson and connect to the Amasa Back trail for your descent once you've completed Rockstacker.
0.0 Exit parking, uphill on road N38 31.710 W109 35.705
0.6 Drop R off road N38 31.435 W109 36.096
0.8 Cross creek N38 31.589 W109 36.080
2.8 Top of climb, for now N38 31.079 W109 37.115
3.5 Pass Portage connector, keep straight
N38 31.721 W109 37.678
3.7 Keep L at fork to Jackson ST
N38 31.761 W109 37.756
4.4 Keep L on Amasa at Pothole fork
N38 31.876 W109 38.369
5.1 View - End of Amasa - backtrack
N38 31.678 W109 38.871
6.2 Alternate joins on L, unmarked
N38 32.047 W109 38.661
7.0 Keep L and straight (R=Rockstacker)
N38 32.533 W109 38.449
7.8 R 100 ft to Pothole Arch N38 33.115 W109 38.447
then back and go north
8.0 Viewpoint, turn around N38 33.228 W109 38.545
9.0 Back at fork. Go R on Rockstacker!
N38 32.533 W109 38.449
9.1 First scary plunge. Yikes!
N38 31.748 W109 37.594
(R = 0.1 mile climb to Amasa, bailout!)
11.8 Cliff exposures. Walk, you fool!
12.8 At Kane Creek, turn R along creekside
N38 31.935 W109 36.152
13.0 Cross creek, go left N38 31.904 W109 35.947
13.1 At Kane Springs parking area
N38 31.945 W109 35.948
R uphill on road
13.6 Back at parking
I'd do Rockstacker again. But at the Jackson Singletrack I'd ride up and over the rise to descend Amasa.
Printable one-page riding guide
GPS track files (right-click and select "Save Target as..."):
Area trails GPX
Topo map for printing: High-Res
Lodging, camping, shops: Link to Moab area resources
Head south on Moab's Main Street. When you reach the McDonald's on your right, turn right onto Kane Creek Blvd. After 0.6 miles, go straight where the road seems to turn right (500 West). Drive along the Colorado River about 5 miles until the road turns to gravel, and head uphill about 2/3 mile. Watch for the "Amasa Back Parking" area at GPS N 38° 31.329' W 109° 35.501'. Head further up the gravel road 1/2 mile, and turn right onto the trail at the sign.