But, why do we have mountains and prairies in Colorado instead of, say, rain forests or oceans? Here, in a nutshell, is how the current scenery emerged.
Out of Chaos
Colorado was once part of the Western Interior Seaway that divided the continent from north to south. About 70 million years ago, the East Pacific tektonic plate began to shift to the east and slide under the North American plate, creating massive uplifts, folding, and faulting (translate that as mega-earthquakes). Through the cracks and crevices, volcanic pressure was released in gigantic eruptions of molten lava. This long period of chaos, interspersed with quieter eras of erosion and settling, gave birth to the Rocky Mountains that run north to south right through the middle of Colorado.
During these eons of activity, the area to the east of the mountains was also being tilted much more gradually. The old sea bed became a very long slope that drops about ten feet per mile, creating the Great Plains from the mountains to the Mississippi River. On the east slope of the mountains, water drains into tributaries of the Mississippi, then south to the Gulf of Mexico. On the west slope, water drains to the Colorado River and its tributaries and south to the Gulf of California. The dividing line between east slope and west slope is the Continental Divide, which follows a crooked line from north to south through the mountains.
Climates shifted and changed, and for a long period the land supported dinosaurs, mammoths and saber-toothed tigers - but more about those in future articles about Dinosaur National Monument and the Florrisant Fossil Beds.
From Fire to Ice
The final touch to this immense mountain-building episode began about two million years ago during the Ice Age, when continental ice sheets covered much of North America. Ice caps and glaciers formed on the mountains. Several periods of freezing, then melting, followed.
Receding glaciers scoured out whole sides of mountains and as they slowly moved down slope with their abrasive loads of rocks and dirt, cutting valleys and great bowls known as cirques. One of my favorite cirques is the vast bowl on Mount Ypsillon in Rocky Mountain National Park.
On a much smaller scale, glacial periods continued into the 18th century. The most recent advance began about 300 years ago along the Colorado Front Range and lasted until the mid-1800s when the climate began a warming trend. Only a few cirques with glaciers or large perennial snowbanks still contain small ice cores from this era.
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