Nephi's Twist
The official Nephi's Twist trail is a doubletrack heading up a wash from La Verkin Creek to the Moenkopi Trail. It's about 1.5 mile long, and has a ridiculously steep section near the upper end. If you're doing the official ride, I'd suggest downhill only, or as an out-and-back from the bottom doing only the first 0.8 mile. The Nephi's Twist singletrack is an experts-only romp along a ridgeline of Moenkopi clay. It starts on a spur off the Moenkopi Trail and connects to Nephi's Twist DT about 0.7 miles up from the bottom trailhead. The fun stuff is 3/4 mile in length. The ride can be done as a 3-mile DH with shuttle (or with a 3-mile road return), or as a 2-mile loop (with a stiff climb vs push-a-bike).
Riding notes, ST from the top:
0.0   From the shooting range sign, head north on DT
Immediately keep R N37 13.683 W113 15.188
(L=DT to bottom)
0.2   Keep R N37 13.793 W113 15.212 (L=alternate to downhill DT)
0.4   Fork L off Moenkopi on DT N37 13.950 W113 15.222
0.7   At high point of DT, find trail on left N37 14.048 W113 15.495
(Trail will wrap around to the south side of the small knoll)
1.1   South (L) on ridge N37 13.955 W113 15.770
(Option: steep plunge R to alternates
split at N37 13.938 W113 15.806)
1.2   Option L on ridge vs R down then L N37 13.897 W113 15.751
(Or R uphill toward alternates)
1.3   In wash bottom heading south N37 13.857 W113 15.791
1.4   At DT, R downhill N37 13.766 W113 15.894
(Option L uphill for loop, or to return to upper TH)
2.0   Fork L N37 13.799 W113 15.380
2.1   L for another loop N37 13.793 W113 15.212
R to return to car  at shooting range
1.5   Keep R downhill N37 13.753 W113 15.956
1.7   Keep R downhill N37 13.744 W113 16.139
(L= to subdivision roads)
2.1   At bottom TH N37 13.893 W113 16.428, turn L
Stay L on paved roads until you reach SR-17 at 2.9
3.9   Traffic light, L on SR-9
5.7    L into parking area
5.8    Back at car
Getting there: From I-15, take either the Toquerville (if southbound) or Hurricane (if coming up from St George) exits. Go to La Verkin. At the traffic light where Highway 9 meets Highway 17, head east (toward Zion National Park).  Exactly 1.7 miles after the light, you'll crest the top of the bluff. Immediately look for the dirt road on the left. Drive 0.1 mile to a broad dirt area. (In 3/08, there was a shooting club sign and a dumpster.) Park here, N37 13.663 W113 15.145. The trailhead is the dirt doubletrack heading straight north (on the left side of the parking area).
Trail conditions change! Use at your own risk.
Bottom trailhead: Heading south after passing through Toquerville, SR-17 descends toward La Verkin Creek. Turn into Trail Ridge subdivision (currently just a bunch of roads). Keep left along the river until you hit dirt road. Park there. The Nephi's Twist trailhead is on the right, about 100 feet from the pavement's end.