Rusty Nail Trail
The Rusty Nail Trail itself is only 2 miles long, climbing from the Gold Bar Rim 4x4 road to the Golden Spike 4x4 route near the Golden Crack. Lowest altitude is 4550, top is 5100. I wouldn't consider this trail to be a stand-alone route -- it's an intermediate that creates some nice combined-trail rides. From the Gemini Bridges trailhead, here are two riding options: a loop, and a point-to-point.
Riding notes, Gold Bar - Rusty Nail Loop clockwise:
0.0   Begin riding Gemini Bridges road
        N38 39.376 W109 40.659
4.6   L on Gold Bar road
        N38 35.997 W109 40.426
5.1    L on Gold Bar ST
         N38 35.881 W109 40.143
6.2    Stay L. Alternate track on R
         N38 36.543 W109 39.961
6.6    Alternate rejoins N38 36.682 W109 39.698
7.1    Straight (R), L=closed area
         N38 36.635 W109 39.295
         Descend toward Gold Bar
7.4    Join Gold Bar rd, fork L
         N38 36.419 W109 39.233
8.8    Keep R (L=return from closed area)
         N38 36.817 W109 38.562
8.9    Straight (L) to viewpoint (R=Golden Spike)
         N38 36.849 W109 38.525
9.0    Viewpoint, backtrack downhill
         In 100 yards, L on Golden Spike
9.9    Fork R downhill on Rusty Nail
         N38 36.508 W109 38.240
11.9  L on Gold Bar Rim road
         N38 36.097 W109 39.341
13.4  R on Gemini Bridges road
18.0  Back at parking
Riding notes, Rusty Nail to Poison Spider:
0.0   Begin riding Gemini Bridges road
        N38 39.376 W109 40.659
4.6   L on Gold Bar road
        N38 35.997 W109 40.426
5.1    Stay on Gold Bar 4x4 as ST crosses
         N38 35.881 W109 40.143
6.1    R on Rusty Nail
         N38 36.097 W109 39.341
8.1    R on Golden Spike
         N38 36.508 W109 38.240
8.4    Golden Crack N38 36.509 W109 38.138
9.1    Overlook N38 36.529 W109 37.550
10.5  Straight (L) N38 35.884 W109 36.815
10.8  L to Viewpoint N38 35.920 W109 36.547
11.6   Keep L N38 35.435 W109 36.506
11.8   Stay straight in wash N38 35.302 W109 36.449
12.7? L for Portal Connector (exact spot not noted, sorry)
14.4   R on Poison Spider  N38 33.710 W109 35.788
15.2   Keep R (L = alternate) N38 33.273 W109 36.233
17.1   Alternate rejoins N38 33.078 W109 36.878
19.6  At Poison Spider parking N38 31.939 W109 36.560
Getting there, Gemini TH:  Drive south on US-191 for 16 miles south of I-70 (about 15 miles north of Moab). Spot the parking area on the west (right as you head toward Moab) side of the road. GPS N 38 39.381' W 109 40.672'. Park in front of the railroad tracks, and head out west on the road. (Note: this is private parking, and requires payment of a fee. Free parking is available across the highway at the Bar M trailhead.)
Start at Gold Bar:  Instead of parking at the Gemini TH, drive 4.5 miles up the Gemini Bridges road. Turn left at the Gold Bar Rim road and drop off to begin your ride.
To leave a shuttle at the Poison Spider trailhead for the point-to-point ride: On 191 at the bottom of the canyon (just past the old tailings pile), turn west onto U-278 (also called Potash Road). Drive 6 miles then turn right up a short dirt road with a sign that says "Dinosaur Tracks." There's a bathroom at the parking area. GPS is N 38 31.917' W 109 36.473'.

Copyright 2011. Trail status can change. Use this guide at your own risk.