The Longs Peak Diamond is among the country’s most spectacular mountain faces. The sheer, 1,000-foot-high wall has been a favorite high-altitude testing ground for experienced rock climbers since its first ascent in 1960, buts its extreme exposure and unforgiving nature routinely necessitate dramatic mountain rescues. The most recent was in early June, when a park helicopter plucked ten Special Forces troops from Fort Carson off the mountain after two of the soldiers contracted altitude sickness while ascending the Kiener Route, which skirts around the Diamond’s left side.

The Diamond’s vertical face is an especially dramatic example of glacial erosion. Five million years ago Colorado’s mountains, including Longs Peak, formed a gently rolling upland, the remnants of which can still be seen today high on Trail Ridge Road. But about 2.5 million years ago, things changed dramatically as the global climate began to cool. The lower temperatures prevented the winter snowpack from melting completely. As subsequent snowfalls piled atop the residual layers, the snow at the bottom was gradually compressed into blue ice, and Colorado’s glaciers were born.

These glaciers formed high in the river valleys, including Roaring Fork, which today drains the east flank of Longs Peak. As in all such valleys, there was a point high in the Roaring Fork’s drainage below which the snow piled up deep enough to create glacial ice; above it, there was too little compression for ice to form. Where it existed, the ice slowly slid downhill, plucking out blocks of rock and dragging them across the underlying bedrock, abrading it like sandpaper and dramatically deepening and widening the valleys. Upstream of the point, however, there was minimal abrasion, so little erosion occurred. This difference created the steep, cookie-bite headwall on the east face of Longs Peak.

Although such headwalls are common in Colorado’s glaciated mountains, none is as tall or steep as The Diamond. Two additional factors contributed to its uniqueness: the unusual strength of the mountain’s granite and the presence of a series of cracks, called joints, in this rock, which are important lines of weakness. All rocks possess joints, but the vertical orientation of those on Longs Peak meant that as the Roaring Fork glacier gouged out the underlying rock, the joints lost their support. Once this happened, rockfall after rockfall tumbled from the face. Because the joints are vertical, the remaining rock wall –The Diamond – became Colorado’s vertical masterpiece.

Terri Cook
Terri Cook
Terri Cook is an award-winning freelance writer based in Boulder. More of her work can be found at