By Michael Dallin
This photograph shows a specimen of metamorphic rock, taken near Emerald Lake.
Metamorphic rock accounts for much of Rocky Mountain National Park. The rock is between 1.4 and 1.7 billion years old. Metamorphic rock is easily distinguishable because of the "layered" effect of minerals within the rock.
Several billion years ealier, the metamorphic rock was sedimentary rock -- that is, they were layers of small grains of sand, limestone, and so on that became "glued" together. Crustal movements of the earth forced these layers of sedimentary rock far below the surface, where pressure and temperature increased dramatically.
These high pressures and temperatures forced the induvidial grains in the sedimentary rock -- which at this point are just "glued" together -- to fuse together. When sedimentary rock is fused, the induvidual grains lock together in new, interesting crystal patterns unique only to metamorphic rock. The pressures caused the layers to bend, and these folds are readily apparent in the park. This fusing and bending process is known as metamorphism, and the end result is metamorphic rock.
Forces within the earth later pushed the metamorphic rock above the surface, exposing the metamorphosed layers.
Occasionally, molten rock seeped into the layers of sedimentary rock as they were metamorphosed. This molten rock eventually cooled down and hardened into granites. These granite intrusions are common throughout the park, appearing as a greyish-white streak across a metamorphic rock face. This can easily be seen on many peaks, including Hallett Peak and Ypsilon Mountain.
Rocky Mountain National Park