This is the standard route up Clarence King's "Obelisk", first ascended by King in 1866. While not one of the High Sierra's most challenging climbs, the quality of the rock, the scenery, the wilderness setting, and the prominence of Clark's graceful granite contours make it a worthy destination.
Whatever contractor Mother Nature hired to ship the rough hewn granite to the Cathedral Range to build those superb mountains also mistakenly left a large load of this granite where Mount Clark now stands. It's that good.
The route can be approached from either the Mono Meadows trailhead or up through Clark Canyon from Happy Isles. These approaches are detailed at length in Bob Burd's description for the nearby Northwest Arete, so they are not repeated here. The most common and easiest approach is from Mono Meadows.
An important factor to consider in making the Mono Meadows approach is the time of year to make the approach. Earlier in the summer, the boggy conditions on the approach shortly after leaving Illiouette Creek can make for slow going and buggy conditions. Later in the year, the progress is easier but the high camp below Clark's sweeping western face is dry so plan accordingly.
This route description is from the camp at about 9,800 below Clark's west face. Coming from Clark Canyon and Obelisk Lake there is no reason to head towards the gap.
From the camp beneath the west face, head up and right through a whitebark pine forest, eventually turning north, heading up easy sandy slopes. At about 11,000 feet, the Secor guide describes a gap in the arete. Perhaps a better way to characterize it is a gap/low point in the ridge as the ridge to the south heading towards Gray Peak isn't much of an arete.
At this gap, there are two ways to proceed. One is to downclimb from the gap (Class 2ish) and turn north on sandy slopes to heading toward the summit. Eventually, after passing a few prominent towers, you will scramble back up to the ridge.
Another more fun option is to simply start climbing the Class 3-4 rock right from the gap. After a few fun pitches, including an easy knife edge, descend north along a 3rd class ledge after reaching an impassable barrier. Shortly after descending, climb back up onto the crest of the ridge.
After regaining the ridge, enjoy more easy climbing on golden granite until reaching King's awkward step-across. After an easy but probably ungraceful move, make the step across and follow a steepish but solid Class 4 pitch to the summit. The summit is a short scramble above.
A good argument can be made that more granite domes, spires, ridges, and faces can be seen in the sweeping view from the summit than anywhere else in Yosemite or the High Sierra.
For those people who prefer protection and a rope on Class 4 like me, bring a few cams and a bunch of slings. Mostly slings are needed for protection.