This is BLM land. There is double track running out of the parking lot. On the right of the lot is single track. Up the double track and to the left is another single track. These routes meet up with each other.
Update 6/13/13:
"This trail system is now fully marked with signage and is very well established. There is even a brand new parking area with bathroom facilities." -wyoexplorer
Take 287 south from Lander and turn towards Muddy Gap/Rawlins. After 8 miles from the turn, you will see tall red cliffs on the left and a small farm with a red rock barn and oil wells to the right. About a 1/4 mile after the farm on the left is a green gate with a graveled lot. Park here.
http://www.singletracks.com/item.php?c=1&i=2651