Arguably the most trafficked and popular hiking trail in the Three Sisters Wilderness, the 4.2-mile stretch up to Green Lakes sees its fair share of visitors. The heavy use is understandable, as it's a spectacular area that offers beautiful mountain views from the shores of a pristine alpine lake.
After only a 35-minute drive from Bend you'll arrive at the Green Lakes/Fall Creek Trailhead. If you have the time, look around the banks of Fall Creek on the south side of Cascade Lakes Scenic Byway. This meadow on the north side of Sparks Lake is not only lush with wildflowers, it also provides some of the most tranquil views of Mount Bachelor.
Once you are on the hike, follow a dusty trail that leads into loose groves of lodgepole pine. As you follow Fall Creek you will quickly ascend into a lush forest dominated by mountain hemlock, and soon a series of cascades will spring from Fall Creek. The subalpine forest thins with elevation gain, and wildflowers, such as magenta paintbrush, lupine and Lewis's monkeyflower, will be on full display.
Before the waters from Green Lakes flow into Fall Creek, they are diverted by a massive obsidian flow devoid of vegetation. William Sullivan, Oregon's hiking and nature laureate, places the flow's development in the context of a volcanic timeline:
"The obsidian flow itself is a sign of South Sister's old age. Young volcanoes typically spew cinders and pour out fluid basalt lava. As a volcano ages, its magma often becomes richer in silica, the mineral in glass. Silica makes the magma so thick that it can clog up the volcano's vent, causing a Mt. St. Helens-style explosion. If that happens, the silica-rich magma froths out as pumice or shatters into ash. If the volcano is dying quietly, however, the silica may ooze out as obsidian-blocks of shiny glass."
Finally, you'll arrive at the saddle between South Sister and Broken Top, where both volcanoes loom over the three bodies of water that make up Green Lakes. The western edge of the basin is composed predominantly of grassy marsh, but a total of 28 designated campsites are sprinkled around all three lakes on the eastern side of the saddle if you are spending the night. Overall Green Lakes makes for an excellent base camp for exploring the high-elevation slopes of the Three Sisters Wilderness. Consider further ascents of South Sister, Middle Sister and Broken Top or continuing roughly 2.4 miles down to Park Meadow.
Note: As is the case at Moraine Lake, it is required to set up camp within 15 feet of the campsite markers due to the area's heavy use. Campfires are also strictly prohibited.