The Green Lakes variation of the South Ridge route provides a great way to climb the summit without putting up with the masses of day-hikers that can often clog the standard route. This route is about 3.5 miles longer each way than the South Ridge route, so factor that into your decision if you want to go for a day hike.
For backpackers, this is a great way to bag both Broken Top and South Sister in a weekend as both summits are easily accessible from Green Lakes.
This trail begins at 5400 feet at the Falls Creek trailhead(also called the Green Lakes trailhead) on the Cascade Highway, between Sparks Lake and Devil's Lake campgrounds. Register at the self-issue permit station and then head north 4.5 miles and 1200 feet up the Falls Creek trail to Green Lakes. The Green Lakes area is settled between Broken Top and South Sister with commanding views of the entire Three Sisters area. This is a great place to camp if you are doing this in two days and allows easy access to both Broken Top and South Sister.
From the Green Lakes area (6600 feet), walk to the southernmost tip of the lake and cross the outlet on a rock/log bridge. Continue hiking west for a half-mile or so along the edge of the lava flow until you reach an area where the trail steepens. You should be able to see a climbers trail picking its way up a loose gravel gully. Climb up this for a few hundred feet and it will flatten out into a nice trail on the left of a small creek. This trail continues practically due west along the south edge of the Lewis Glacier for another two miles or so. Before long, you will be able to see the main trail on the south ridge several hundred feet above you. Eventually, your climbers trail reaches a small circue lake at about 8850 feet and joins with the standard South Ridge route. Follow the hordes of people to the summit from here.
In the summer climbing season, this trail is completely dry so you won't need any gear. Winter and early season climbers will probably want crampons and an ice axe.
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