To reach the LANL fitness trail:
Drive west on W. Jemez road for less than a mile, and turn left onto "Bikini Atoll Rd." (named after an unfortunate island vaporized in the name of science long ago) drive maybe 200 yards until Bikini hits a T-intersection, and turn right. Drive another hundred yards and park in one of the many marked spaces. You're at the trailhead.

Cerro Grande Fire Damage Assessment:
The LANL Fitness trail and subsidiary downhills are still ridable, and were not badly burned (though firefighters conducted some controlled burns in the area to work on the fire line). There is significant bulldozer damage (and a number of new fire roads that are still too dusty and loose to be fun riding) to the first mile of the trail, but the majority is intact. Dickless Trail is in fine shape, though a little more sandy than usual due to the dry weather. Not posted, thus still perfectly legal to ride.

Trail Log:

Please note that this description is of the most direct possible combination of trails. There are other ways to go, but they aren't a whole lot different.

0.0 - Begin riding. Head left on the paved road, and ride 100 yards or so, looking for a singletrack cut into the rock that heads right (west.) Take the singletrack
0.2 - The trail crosses a dirt road. Keep going straight.
0.7 - A trail heads left and back to the east. This is an excellent downhill run, but to stay on the fitness trail, keep going straight.
1.0 - You should come to a paved road with concrete barriers. A trail to the right (the "Dickless Trail") leads back to LANL (an excellent downhill ride that goes .9 miles back to the 0.2 point on the fitness trail.) To stay on the fitness trail, ride straight across the road and onto a singletrack.
1.1 - The singletrack curves around and joins the road to S-site in front of a guard station. Look for a singletrack to the right just past a "warning, US gov't property" sign.
1.4 - A rough old road turns off to the right (the Birth Kanal trailhead is just across the road.) Keep straight.
1.9 - Right onto the singletrack.
2.0 - Right on gravel road.
2.6 - Right on singletrack.
2.8 - Right on dirt road.
3.1 - Right on dirt road.
3.3 - Trail ends at "Parcourse fitness circuit" sign.