Ptarmigan Lake (11,493') is located just west of the Continental Divide in a large bowl off the Tonahutu Trail. The shortest route to Ptarmigan Lake begins at Bear Lake and runs 4.3 miles to Flattop Mountain, where you'll turn north on the Tonahutu Trail to Ptarmigan Pass. Once in this area you can identify the approximate location and descend to the lake.

View from Ptarmigan Pass to Lake Helene and Two Rivers Lake east of the Divide

Cushion and mat plants help build soil by capturing organic debris in their foliage, plots in which grasses and taller plants can eventually root; this turns fellfield into alpine turf, a process that can take centuries

Fellfield occurs on windswept slopes that hold little moisture, with rock comprising up to half the surface

Snowdrift Peak (12,274') stands prominently across the Ptarmigan Lake bowl, a useful landmark that provides a direct line to the lake

Off-trail travel across the tundra is generally mild until reaching the rim of the basin, from which it's a short but much steeper drop to the lake

When wet soil freezes it expands and pushes surface-level rocks up in a process called frost-heaving

Odessa Lake (far center) originates from glacial remnants in the Tourmaline Gorge, which extends east from the Continental Divide between Knobtop and Gabletop

Oxygen percentage is the same at high elevation and sea level (21%); the problem for people is that there are many fewer molecules of everything at high elevation, including oxygen

Tyndall Glacier is a small cirque glacier located between Hallet Peak and Flattop Mountain; keep a safe distance from cornices when viewing the glacier and gorge below

The Flattop Mountain Trail emerges through treeline with exceptional views north across the Mummy Range, which holds some of the tallest peaks in the Park

West-facing slopes with well-developed soil beds support an archetypal collection of alpine grasses such as Blue Grass, Tufted Hair Grass, Spreading Wheatgrass, Kobresia and Pyrennian Sedge

Longs Peak (14,259'), Taylor Peak (13,153') and Otis Peak (12,486') stand prominently to the south along the Continental Divide

Though we mostly associate the alpine region with elk, bighorn sheep and mountain goat, mule deer are equally common at these elevations

Characteristically of the Continental Divide through much of Colorado, the east side drops precipitously while the west side (pictured here) has a gentler slope

Marmots are among the most active alpine mammals in the summer, but enter burrows by early October and don't emerge again until April or May