The South Ridge was first climbed by Ed Cooper and Walter Sellers in July 1958. The route does not follow the ridge crest, but rather traverses below it on the west, then crosses over on the east a few hundred feet below the summit. Nevertheless, it is an enjoyable route with good position the whole way, and reasonably sound rock. The climbing is mostly fourth class for the first two-thirds, then mostly third class once the route crosses over onto the upper southeast face. Confident parties may ascend the route unroped, while others will want to belay some or all of it. Unroped, the climbing above the first notch (see approach below) will take perhaps an hour or two. With fixed belays expect to take several hours.
The route may be approached from either Torment Basin or Boston Basin. Both approaches involve some minor glacier travel and third class scrambling to reach the start of the climb. From Torment Basin ascend slabs to the small glacier/snowfield beneath the southwest face. Cross the glacier to a prominent gully (Class 3) that leads to an obvious notch in the ridge. From Boston Basin contour around a spur ridge from the upper high camp until below the Taboo Glacier nestled beneath the southeast face. Gain the glacier on the left and walk up the left side until a deep gully
appears. Scramble up this (class 3-4) to the notch. ~1 hour from upper high camp.
From the notch ascend a short, steep crack about twenty feet until it is possible to scramble down and left on fourth class ledges to an alcove below a massive gully/chimney. Eschew the gully and climb a dihedral on the left to its end (~100 feet). Climb straight up over a steep section (easier than it looks) until the angle backs off, then trend up and left beneath a headwall (do not
traverse right back into the chimney/gully). Continue working your way up and left for several hundred feet until reaching a third class gully that leads to a notch in the south ridge. The climbing between the dihedral and the notch is mostly fourth class, with bits of easy class five here and there. From the upper notch traverse across and up the southeast face on grassy ledges until directly below the saddle between the north and south summits. Scramble straight up to the saddle then climb the short ridge to the higher south summit. Above the second notch the climbing is mostly third class, though the exposure may feel rather thrilling.
Due to the easy nature of the climbing, and ample opportunities to set up belay anchors, I have opted to describe the route in terms of features of the terrain rather then pitch-by-pitch. Parties desiring the security of a rope may want to consider doing the first twenty feet out of the notch as a short pitch, followed by the short traverse to the start of the dihedral. A belay at the top of the dihedral is also a logical choice. Beyond that, the terrain allows considerable flexibility.
If you came from Boston Basin, then the most logical choice for descent would be to scramble down the Southeast Face to the glacier below. The first two thirds of the descent is third class. The last third above the ice is a bit steeper. Some rappels (rap anchors abound) will get you past this section if you don't feel like downclimbing. From the glacier retrace your steps back to camp or the car.
Returning to Torment Basin is less convenient. Beckey recommends reversing the route, though due to the considerable amount of traversing involved, this could well take as long as the climb up. Scramble back down the way you came until reaching the upper notch. Cross back over to the southwest side and decide what your strategy will be. Rap anchors abound along the route, and many can be seen far below. Since we didn't descend this way, it wasn't clear to us whether these represented established descent routes, or just bail slings. If you are unsure, you could simply downclimb the route back to the top of the dihedral and then rap from there.
Alternatively, descend the Southeast Face to the glacier, and from there walk down slabs along the east side of the South Ridge until it is possible to cross over into Torment Basin via a class 2 saddle.
Usual clothing for a Cascades climb. Helmet is a must. The route can easily be done in mountaineering boots, though some may want to brng their rocks shoes. Depending on the season, ice axe and crampons, showshoes or skis may be needed on the approach to the lower notch. If climbing roped, a 50m rope is more than sufficient. A light alpine rack with gear to 2" should suffice.