From exit 39 on I-80 head South towards Mountain View on route 414 for 6 miles. At the “Y” (@ the Bronze Elk) stay right on route 410 heading towards Robertson at about 6.8 miles on 410 the road makes a 90 degree right hand turn, at this point you will want to go straight (or left) leaving 410. The road turns and stays gravel for the duration of the drive to the trailhead. Continue straight on the gravel road after leaving 410 for 12.3± to another intersection at this point turn left, right would take you to China Meadows (7 miles). After taking the left continue for 7.7± miles to a hairpin turn, at this point continue straight (or right) off of the previous road. Follow this for 3 miles to the Henry’s Fork Trail head. The last 3 miles of the road are not maintained in the winter months, so your temporary trailhead will start 3 miles sooner.
The Henrys Fork Trail is very well used and is easy to follow. From the trailhead, follow the trail south for two miles to a junction. Stay left on the main trail. After another 3.5 miles, you will reach Elkhorn Crossing, where there is a bridge, and another junction; this is the North Highline Trail. Turn right here, and west on the trail posted for Henrys Fork Lake (at least this is what the sign said in 1991). Follow the trail west for 1.2 miles to another junction near Bear Lake. Turn left here for 3 miles and follow the trail to Henrys Fork Lake.
From Henrys Fork Lake, follow the creek feeding the lake for one mile to Lake Blanchard, which is just above timberline.
From Lake Blanchard, head northwest and towards the highly visible Castle Lake Peak, aka Castle Butte, which is not named on the map, but very obvious. You could follow the creek up from Lake Blanchard, but the area is very marshy, and I would recommend staying well east of the creek.
One you are near the little hill labeled 11,434 on the map (make sure to take the short side trip to Castle Lake for some photos), head west and towards the little basin and east of BM 12,679. Once in the basin, just head up the very minor gully, or up the little ridge to the east of the gully (see photo), to the north ridge of Mount Powell. Once on the north ridge of Powell, follow it south to the summit. The summit is 2.2 miles from Lake Blanchard.
You can also ascend/descend Powell’s east face from/to Lake Blanchard, skirting a cliff on the south, but this route is quite a bit steeper.
Total round trip distance is 26 miles with 4000 feet elevation gain, and usually takes three days round trip.
Mount Powell from Henrys Fork Basin.
A good pair of boots and backpacking gear is needed.