Warning! For expert riders only! This trail has it all. Steep climb on a dirt road following some sweet technical single track and finally leading to a beyond scary technical descent. I would only recommend this trail to people with stong technical skills and a beefy bike with more than 5" of travel. I started at the bottom of the Ghost Town of Grafton because i like to do my uphill first and parked next to the cemetary. Dont attempt to ride up the singletrack. I rode the dirt rode up in a clockwise direction and made it a loop.
In La Verkin, turn toward Zion National Park on Highway 9. When you get to Rockville, drive until you're seeing the end of town then turn south (right) on Bridge Road. Cross the Virgin River on the old bridge. Follow the road as it veers right (west). At the fork in the road 1.5 miles later, turn left and park near the wash. Start riding south uphill on the Smithsonian Butte Scenic Byway (may or may not have a sign). If you're shuttling to the top, it's the last doubletrack (on your right) before the top of the mountain, 4.4 miles up, just after the road has turned south again. N37 07.683 W113 06.131
http://www.singletracks.com/item.php?c=1&i=2955