ApproachFrom Mono Meadow
From the trailhead, hike northeast for 3.6 miles. Pass the Buena Vista Trail junction and cross the Illilouette Creek by either wading or using downed trees east of the trail. The creek flows wide and not very deep where the trail crosses it. In mid June on a normal year it is only two feet at the deepest point - much better than circumventing the crossing by using the bridge downstream at Illiloutte Falls. On the other side of the creek the trail heads north through a sandy open area. In two hundred yards a trail junction is encountered - turn right and go east (toward Ottoway Lakes) for about 3 miles, passing Mt. Starr King on your left. The trail skirts some granite cliffs before crossing the Clark Fork of Illilouette Creek. Leave the trail before crossing the creek, and head east (the trail heads south then southeast, following Illilouette Creek).
You are now in a swampy area with a gajillion downed trees and most of the standing ones equally dead. Travel through here is very slow and very tedious. Lesser mortals have given up shortly after getting lost in this quagmire. Mt. Clark is visible from this point, but it is easy to get off-route. Once you are back in the live forest area, the peak will no longer be visible. Some parties end up on Gray Peak by accident. Have a compass and use it. Mt. Clark is ENE from the swamp, not east (that's how you get to Gray Peak). You can follow the Clark Fork to it's headwaters on Mt. Clark, but you will curse every downed tree in your path and pray for logging to return to our National Parks. Your best bet is to stay just north of the swamp on drier ground where you can travel easier through standing trees (you will still pass through some swamp). Aim for the steeper forested slope between two granite bulges that hide Mt. Clark behind them. Pass through the shallow saddle at the top where you will get your first close views of Mt. Clark. While impressive, it is still 3 miles away.
Traverse along the hillside to keep from losing elevation, and head up the wide canyon on Mt. Clark's west side. Having lost sight of Mt. Clark again, it is easy to get off-route a bit and end up at the far north end of the very long NW Arete. A compass is useful here to keep you on track. Climb up endless steep slopes for two miles (over 2,000 ft of vertical here). Eventually you will find yourself before the massive West Face. The NW Arete is on the skyline in front of you. Climb up to the ridge and take in the breathtaking sight of the sheer cliff on the east side.
From Happy Isle
Take the JMT out of Happy Isle following the Merced River up the canyon (the Mist Trail between Vernal and Nevada Falls is a nice alternative with less distance and better views than the JMT proper, but many, many steps!). Around mile 8, just past Bunnell Point and after crossing the twin bridges, the trail begins to climb on the south side of the river. Where it levels out at some granite slabs and before it begins to descend back to the river, leave the trail heading south-southeast.
Climb steeply for 1,000ft under forest canopy, avoiding the brushy area halfway up. If you aren't watchful you will end up in bushwhacking hell (I did, and it cost me!). A flat spot is encountered then more slopes that stay sustained until you reach the toe of the NW Ridge. A large lake with good camping can be found at the base of the cliffs here. Hike southeast into Clark Canyon if you want to climb the east side of Mt. Clark, otherwise head right around the cliffs and climb the ridge that snakes its way for a mile to the NW Arete. There are two minor highpoints along this ridge that can be avoided by contouring around the west side. Or climb them for some extra class 3-4 fun.
Route DescriptionMost of the NW Arete is an extremely exposed class 3 traverse. It is easy climbing, but the exposure can make it seem much more difficult.
Getting onto the arete is the hardest part. There is a wide gully on the NW side (on the right of the arete) that can be climbed a good distance before climbing up to the arete proper. There is often a snowfield in this gully even late in summer, and it is usually easier to move left onto the arete shortly after reaching the snow here (see photo below). Without significant snow in the gully, it can be climbed nearly to the summit on enjoyable rock up to easy class 5.
There are at least three places that you can use to move from the gully to the arete, all of them seem class 4 or harder. Some parties use a rope here, but there is little exposure on this short section and carrying a rope all the way to Mt. Clark is quite painful (we did, and never used it!).
Once on the arete, stay right on top for most of the way, dropping down on either side in a few places. There is one main obstacle to get around on the right side of the arete, requiring a bit of crack and face climbing along with a bit of squirming to get around a large block overhead.
There is some easy class 4 just before the summit to climb up to the highest point. This is again on the right (west) side of the arete.