Clark Mountain is one of the highest peaks in the North-Central Cascades of Washington. It is roughly 50th highest in the state depending on the list you go by. Since it is the farthest south of all the northern Washington Top 100 peaks, there are no nearby high peaks to its south. As such, when you get to its top, it seems to tower over the lower hills to its south much like Mt. Rainier towers over its surroundings. At least that's the impression I got.
Seven miles to the WNW of Clark is the stratovolcano Glacier Peak (10,541 ft), of which many a summitposter is familiar. Clark and Glacier are connected by a long high ridge. This ridge is known as the DaKobed Range. (DaKobed means "Great Parent" and was an Indian name for Glacier Peak.) Other major peaks along this ridge include Luahna Peak (est. 8,450 ft), Chalangin Peak (est. 8,350 ft), Tenpeak Mountain (8,281 ft), and the Kololo Peaks (8,200+ ft).
Clark Mountain is characterized by rugged, open south and west sides and glaciated north and east flanks. The vertical drop from the summit to the White River on the southwest is an impressive 6,100 ft in about two miles. The drop to the northeast to Napeequa River is 4,100 feet in about two miles. There are two important glaciers eating away at Clark. The first of these is the Walrus Glacier (shown as the Clark Glacier on maps) on the east. It is about 3/10th of a square mile in area. When it is in shape, this glacier is a semi-popular basic glacier climb for the Mountaineers.
The second but larger glacier is the Richardson (1.4 sq. mi.) on the northern flanks. The Richardson Glacier pinches in between Clark and Luahna and extends up to Clark on a second tier.
To get to Clark Mountain, it is standard to approach by way of the White River Road. See the next paragraph for how to get to the White River Road. This road ends at 2,300 ft about 5 miles south of Clark. Take the nearly flat trail for about 4 miles to the Boulder Creek Trail junction at 2,540 ft. From here, you can go one of five ways to Clark: 1) Boulder Creek, 2) the slabby watercourse coming down from the upper South Basin of Clark, 3) Thunder Creek to the west, 4) Walrus Glacier, or 5) Richardson Glacier.
From U.S. 2 (Stevens Pass Highway) at Coles Corner (westbound, ~13 miles from Leavenworth), go north on SR-207. There are two tricky Y-intersections in about 4 miles, but the basic idea is to stay left so that you eventually begin driving past the north side of Lake Wenatchee. This is the White River Road. At the northwest end of the lake, pass the tiny hamlet of Telma (1910 ft). About a mile past Telma there is a junction. Go right to continue up WRR. In about 11 miles from the junction, the road ends (~21 miles from U.S. 2). It is paved for maybe the first half.
1.) Boulder Creek. For a good trip report for this route, see Eric's Base Camp. Essentially, you want to take the Boulder Creek Trail about 4.5 miles to the 5,000-ft level near the head of Boulder Creek Basin then locate and ascend an old sheepherder's trail westward to about 5,600-5,700 ft, whereupon you'll need to leave it and trek cross-country on a roughly NNW bearing on open heathery terrain to the crest of the south spur coming off of the SE Peak of Clark (Pt. 8373).
It is then critical to find the one and only easy gully off this crest into the South Basin of Clark. It is somewhere between 7,200-7,300 ft on the crest. From the crest you will be able to see the main summit of Clark. Drop down the gully a couple of hundred feet and then contour the upper South Basin on crappy rock and some perennial snow to the final South Ridge. A fast party should be able to go from car to summit in 7 hours. It is non-technical all the way though the gully at 7,200 ft can become icy in October. Roughly 11 miles from car to summit.
2.) Y Basin. On the maps there is a creek shown coming out of the South Basin of Clark. The upper part of the creek branches into two tributaries (the Y). We ascended this watercourse directly from the White River Trail. Leave the trail at ~2,560 ft when you can see the slabby objective watercourse. This is about where the 'e' is in "White" on maps. The bushwhacking to get over to the watercourse is inconsequential (mostly you can follow a streambank or step through waist-high brush). For the first 800 ft or so we ascended and traversed class 3 slabs on the west side of the stream. After that, we were mostly on the east side.
There were only a few harder class 4 moves to get up steps, but mostly it was fast, efficient travel. At around 4,900 ft the slabs end and the basin opens up to steep grass and heather slopes. The SE Peak of Clark (Pt. 8373 will be above you). From here, you want to take the left (west) fork of the creek all the way to the upper rocky basin then take a left for the final South Ridge of Clark. This is a steep direttissima route to the summit (6,100 feet in 2.5 miles), but it is good because it doesn't mess around going this way or that way (unlike Route 1 described above). Roughly eight miles from car to summit.
3.) Thunder Creek. Note: this route can be notoriously difficult to locate on the way up but is very feasible as a descent route. About 7 miles from the car (2.7 miles past Boulder Creek junction) when the White River Trail is in a section of heavy timber will very minimal undergrowth, the trail will go past a large cut log (a section of the log on both sides such that their separation is about 20 feet). Leave the trail here (2,800 ft to 3,000 ft) and bear north perpendicular to the trail. Search for a sheepherder's trail about 100 feet north from where you left the main trail. You might have to look back and forth for it for a short time. But once you find it, this trail, which is in pretty good shape down low, can be taken practically all the way to the crossing of Thunder Creek at 3,750 ft.
Cross Thunder Creek and head immediately east to the prominent timber rib coming down to the creek. Do not go left of the timbered rib because it is very very brushy. Ascend the timbered rib to its top at about 5,800 ft. This rib melds with the southwest spur of Pt. 7970 (the rock point immediately northwest of Clark's summit). At 5,800 ft, contour right into the upper West Basin of Clark and ascend to the summit. The final few hundred feet is on total choss. Find and climb a steep, loose gully to the final South Ridge. Maybe about 11 miles from car to summit. Non-technical all the way.
4) Walrus Glacier. Take the Boulder Creek Trail over Boulder Pass or approach by way of the Nepeequa River Trail over Little Giant Pass. These two trails merge at the Napeequa River about 3.7 miles east of Boulder Pass. Take the NRT about one mile north, cross the river, then ascend brush, heather, slabs, and morainal debris to the glacier. Ascend the glacier as guidebooks or conditions dictate.
5) Richardson Glacier. Approach as per Route 4 above but instead go a mile or so farther up the trail. Follow guidebook recommendations as to the approach to the glacier. Having not seen this route first-hand, I hesitate to give theoretical information.
Clark Mountain is located in the Glacier Peak Wilderness so standard Wilderness policy applies (no machinry, etc.). Camping permits are not required. Sites are first come first pitched.
You could climb this peak at any time of year provided you could get to it. The White River Trail only goes as high as 2,500 ft by the time you have to leave it, so it is likely you could at least get to the foot of the mountain later in the fall or earlier in the spring than other high peaks. However, there is much evidence of avalanching, so being in there in winter would necessitate perfect conditions. The flanks of the peak are steep, so be prepared for some steep snow slogging. As a ski tour, it could be a worthy objective, particularly for the Boulder Creek Route.
You could camp just about anywhere if you could manage it. There is a large camping area at the Boulder Creek junction and again another one in the vicinity of Thunder Creek. Once you get higher up the mountain's sides, flat ground becomes more of a premium but such flat spaces certainly do exist. For campsites for the glacier routes, I defer comment having not been over that way. But if you're hardcore enough to do a glacier route, you don't need a luxury campsite anyway.