10. Maroon Lake, Colorado
These hills are “The Dangerous Bells” that alert the daring climbers of “down sloping, and unstable” stones that “kill without warning”. Compared to other mountains in the Rockies, made of limestone and granite, the Bells are made of metamorphic sedimentary materials that have solidified into stone over an incredible number of years. Mudstone is brittle and is broken easily, alarmingly producing loose stones along almost any path.