Unlike other mountains in the Rockies that are composed of granite and limestone, the Bells are composed of metamorphic sedimentary mudstone that has hardened into rock over millions of years.
 Mudstone is weak and fractures readily, giving rise to dangerously loose rock along almost any route.
A US Forest Service sign on the access trail warns would-be climbers of "downsloping, loose, rotten and unstable" rock that "kills without warning".
The mudstone is also responsible for the Bells' distinctive maroon color.
 The Bells got their "deadly" reputation in 1965 when eight people died in five separate accidents.

Maroon Lake elevation 9,580 ft (2,920 m) occupies a basin that was sculpted by Ice-Age glaciers and later dammed by a landslide and rockfall debris from the steep slopes above the valley floor.
Unlike other mountains in the Rockies that are composed of granite and limestone, the Bells are composed of metamorphic sedimentary mudstone that has hardened into rock over millions of years.  Mudstone is weak and fractures readily, giving rise to dangerously loose rock along almost any route. A US Forest Service sign on the access trail warns would-be climbers of "downsloping, loose, rotten and unstable" rock that "kills without warning". The mudstone is also responsible for the Bells' distinctive maroon color.  The Bells got their "deadly" reputation in 1965 when eight people died in five separate accidents.
Maroon Lake elevation 9,580 ft (2,920 m) occupies a basin that was sculpted by Ice-Age glaciers and later dammed by a landslide and rockfall debris from the steep slopes above the valley floor.
Maroon Bells