1) Pacific Crest Trail (PCT) - This is the most common approach for the south ridge. On Hwy 20/26 in Santiam Pass the summer trailhead is well marked with a sign on the north side of the road. Parking is just under half a mile from the highway. Follow the PCT north 5-6 miles, usually about 3 hours.
There is also a Square Lake / Booth Lake trail which branches off the PCT near the trailhead. It has little merit in summer as it is hot, dry and dusty. There is no trail to the base of the mountain, cross country travel is required from the trail to the SE bowl. This is a viable approach for the SE Couloir in winter.
The winter trailhead is a mile or so further west along US 20/26 in a well marked and heavily used snowpark. Start here and follow a trail parallel to the road to reach the summer trailhead (which is not plowed).
2) Jack Lake Road (USFS 12) - This is an alternate approach from the east side. Turn north onto USFS 12, signed as Jack Lake Road, seven miles east of Santiam Pass and 12 miles west of Sisters.After 4.5 miles turn left onto 1230 where the pavement ends and in another 1.6 miles stay left on 1234. The roads are marked and gravelled.
Follow Canyon Creek / Wasco Lake trail about 10 minutes to the wilderness boundary. Stay left to Canyon Creek Meadow, which offers some scenic camping possibilities. To go to the south ridge cross a gap in the east ridge which usually has a nice little tarn in it. After this gap traverse and climb the scree slopes to the low point in the south ridge. This approach may have snow Later in the spring than the PCT. In the bowl it can often be avoided on the climbers right, although this puts one close to the east face which sheds rocks frequently.