St Mary's Glacier is located north of Idaho Springs in the Clear Creek Ranger District of the Arapaho National Forest. The glacier – technically a large perennial snowfield – is a popular year-round destination open to hiking, skiing, glissading, climbing and sledding. St Mary’s Lake, located just below the glacier, is ringed by bristlecone pine, thick willow and a bright collection of summer wildflowers.

There are 2 basic types of glaciers: 1) valley glaciers that creep downslope via gravity, and 2) continental glaciers that flow outward from a thick central area under their own weight

The Rockies have been shaped by the cyclical growth, recession and reconstitution of glaciers over many millennia

Scientists generally recognize bighorn sheep as 1 species with 3 subspecies: Rocky Mountain, Sierra Nevada and Desert

Bristlecones may take a century to add just 1 inch in diameter, and can become nearly dormant during a drought

Fireweed along the north edge of St Mary's Glacier; fireweed is often among the first flowers to occupy disturbed land

A true glacier is in constant motion, and ice in the accumulation zone flows down to lower points called the ablation zone

St Mary's Lake supports a naturally reproducing population of brook trout

St Mary's Glacier tapers up a narrow gluch that levels in open tundra

St Mary's Lake is ringed by bristlecone pine, a species adpated to high elevations and extreme environments

The snowfield drops steeply to the edge of St Mary's Lake, a scenic but precarious section

Mount Bancroft (left) and James Peak (right) seen from open tundra above the glacier

Early morning reflections in St Mary's Lake