The directions to Beaver Basin on this page are incomplete. These should be helpful:
From the turnoff to Castle Valley on Hwy 128 it is approximately 25.8 miles to Beaver Basin. Reset your odometer here. A high-clearance vehicle is required to make it all the way to the Basin.
Follow the main road (Mountain Valley Rd.) southward as it gradually gains elevation toward the mountains. The road turns to dirt at approx. 16.2 mi. Stay left as the pavement ends.
At 18.4 mi. turn right onto FR 107. At approx. 20.9 mi. take another right, after which you will soon pass a large forest service sign. Continue on this road to a fork at 22.2 mi. Stay right at the fork. After 1/10th of a mile you will see the sign for Don's Lake at another fork. Stay right at this fork, too.
At approx. 23.1 mi. the road forks once again, and as before, stay right.
At 23.5 mi. the road makes a sharp uphill u-turn to the right. In late July 2013 the top of the turn was narrow and eroded enough to make travel a little uncomfortable.
At 23.8 miles you will encounter the roughest section of the road. Very slow going at this point.
At 24.8 miles you will come into the first clearing where camping is feasible. Continue down the road the last mile for better campsites at the actual trailhead.