Although this route is titled Southfork Pass, the route really describes the ascent via south slope which is composed of chutes and ribs. Most people will approach the south slope via the pass but it can also be approached from the Palisade Lakes on the John Muir trail. The south slope is composed of formidable ribs and loose chutes, most of which deadend before reaching the summit. The correct route ends at the easier class 2 southeast talus slope that takes you directly to the summit.
The approach to Southfork Pass starts at the South Fork Big Pine trailhead. After reaching Brainard Lake, you have the option to ascend to Finger Lake and take the east Finger Lake inlet to a notch on the east ridge or ascend directly from Brainard via a drainage that comes down from two nameless lakes further up. Both get you to the foot of the pass about the same time. The pass is actually composed of two chutes: the closer but more difficult east chute or the farther but easier west chute. Scramble to the top of the pass to access the south slope of the Thumb.
From the south side of the pass, traverse horizontally across the loose south base of the Thumb until you're close to the southeast ridge. Enter a wide but extremely loose chute until it begins to significantly narrow. An exit to the right (marked by large cairns) takes you into another chute. This chute quickly ends in a variety of options from loose, narrow chutes to fun, class 3 rock climbs. All options end on top of the ridge which forms the left side of the easy class 2 southeast slope. Climb up and to the right skirting the hanging block sub-peak on the right to the top.
Ice ax and crampons are needed to ascend Southfork Pass. Late in the season, it may be possible to skirt snow by climbing on the rocks on the right. The south chutes are usually snow free during summer months.