Leatherman Peak, Lost River Range, Idaho
Driving Directions for West Fork Pahsimeroi Road  (the eastern ridge approach via Leatherman's north gully and the route we used)

We used Trails of Eastern Idaho by Margaret Fuller and Jerry Painter, 3rd Edition.  Published in 2010 by Trail Guide Books.
BE PREPARED WITH DETAILED MAP, WATER, VEHICLE IN GOOD CONDITION (4WD PREFERABLE TO MAKE IT LAST MILE TO TRAILHEAD, OTHERWISE WITHOUT A 4WD WILL HAVE TO WALK LAST MILE TO TRAILHEAD).  THIS IS A VERY ISOLATED AREA, TRAVEL AT YOUR OWN RISK.  GPS RECOMMENDED.

Lat/Long of trailhead at end of West Fork Pahsimeroi Road:  44.1292 N    113.7271 W
Here is a combination of that description with my notes out of Mackay, Idaho:

• Drive 17.5 miles north of Mackay on US 93 to Doublesprings Road (#116), between mile markers 131 and 132. 
• Turn east on this road (zero your odometer) and drive for 10.5 miles to an intersection with Horseheaven Pass Road #117.  You will have gone over Doublesprings Pass at 8,310' elevation.
• At the intersection of #116 and #117, there is a brown sign that has Carlson Lake on it.  Turn right (south) and continue on Horseheaven Pass Road.
• At mile 11.6, an intersection with road heading left goes to Carlson Lake; keep right at "Y" intersection.  You will be heading southwest in a valley toward a large limestone cliff on your left.
• At mile 14.3 you pass over Horseheaven Pass (unmarked) and start descending down into wide valley.
• At 16.7 miles, a road from Burnt Creek joins from the left; keep straight.
• At 18 miles, the track descends into Mahogany Creek, with water running in it (not very deep when we went), and up out over a hill.
• Keep straight ahead ( don't go on side road through a gate).
• You will see a steep hill, but to avoid it, there is a bypass:  keep right and then turn left to rejoin the main road above the hill.
• The road then descends into the valley of the Pahsimeroi  River.  At 21.1 miles, (Fuller's book says 21.8 miles), you pass close by a cattleman's cabin.
• At 21.3 miles you come to a sign for West Fork of Pahsimeroi and East Fork of Pahsimeroi.  Take the right (north) branch #267 to the West Fork of Pahsimeroi River.  
• High clearance is essential because road is narrow and rocky.  Some vehicles without 4WD may want to park here.
• The trailhead is another rocky one mile: the road ends at a clearing with a campsite along the West Fork of the Pahsimeroi River.  The trailhead sign for Pass Lake and Merriam Lake is at the end of this clearing.