J-Boy Trail
The J-Boy Trail lies on the eastern end of the Red Fleet mountain bike trail area. It's 2.5 miles long with around 800 vertical feet of elevation change. J-Boy can be done as a short loop (see below) or as part of a longer ride when combined with other area trails. It connects to Handsome Cabin Boy and Three Amigos.
Trail connections, alignments, and conditions will change. Use this guide at your own risk. 2016 UtahMountainBiking.
Riding notes, little J-Boy loop:
Dinosaur Tracks trailhead
0.0   Dino tracks trail N40 35.740 W109 26.178
        100 feet, fork R on J-Boy
        N40 35.720 W109 26.188
0.6   View, highest point
1.2   Hard R on HCB
        N40 35.848 W109 26.657
1.4   Cross road to slickrock
        N40 35.925 W109 26.403
1.7   R downhill on J-Boy
        N40 36.032 W109 26.225
2.0   Cross road to parking
Riding notes, HCB/JB/JCM loop:
Jazz Chromoly trailhead
0.0  Exit parking, L on paved road
       N40 35.923 W109 27.470
       100 feet later, R on narrow ST
       N40 35.926 W109 27.430
0.6  Keep straight R (L=bailout to road)
       N40 35.720 W109 26.896
0.7  Fork, L through wash and up rock
       N40 35.619 W109 26.858
1.0  Climbing eases 
       (you've done 200 vertical in 0.4 mi)
1.1  Fork R to J-Boy)
       N40 35.847 W109 26.653
1.7  Viewpoint, begin descent
2.2  L uphill on road 100 feet
       R to trail  N40 35.740 W109 26.178
2.6   Veer R (rejoin HCB)
        N40 36.031 W109 26.219
3.1   Keep R on J-Boy (L = HCB)
        N40 36.351 W109 26.127
3.3   Keep L (R = Three Amigos)
        N40 36.408 W109 26.268
3.5   Fork L N40 36.256 W109 26.412
3.6   R up to paved road
        N40 36.181 W109 26.373
        Cross road
4.0   Cross road and cattlegrate
        N on ST N40 36.142 W109 26.621
4.1   Join Jazz Chromoly, keep R
        N40 36.238 W109 26.713
4.8  Turn L (west) N40 36.784 W109 26.862
5.7   Rightmost fork
        N40 36.550 W109 27.397
6.3   Alternate rejoins on L
        N40 36.094 W109 27.626
6.4   Fork hard R 
        N40 36.033 W109 27.728
7.0   Keep R N40 35.955 W109 27.894
7.8   Back at parking
Getting there...
Jazz Chromoly Trailhead:
In Vernal on US-40 (the main drag), turn north on US-191. Drive to mile 10.7 and turn right at the paved road signed "Red Fleet Dinosaur Trackway." Drive uphill 0.6 miles. At the top of the hill, turn left onto a dirt road and immediately park in the wide area on the left. On your bike, go back to the paved road and turn left. 100 feet later, find the narrow Handsome Cabin Boy (HCB) singletrack on the right (south) side of the road, heading south. J-Boy is found 1.1 miles along HCB.
Cattle grate parking:  Drive to the cattle grate at mile 1.5 and park in the small spot on the right side of the road. Find Handsome Cabin Boy southbound along the fence and follow it until it crosses the road again. J-Boy forks left immediately as the trail leaves the road.
Dinosaur Tracks trailhead:  Drive to the Dinosaur Tracks parking area at mile 2.4 from US 191. J-Boy is across the road from the uphill end of the parking strip, and also 100 feet down the dinosaur tracks hiking trail.