Geologic Processes

Beginning millions of years ago, the Rocky Mountains went through many geological changes as they formed. A period of intense plate tectonic activity caused the rugged landscape of much of western North America, especially the Rocky Mountains. Through continental collisions, plate subductions, and erosion, the Rocky Mountains were slowly shaped into the grand national park that attracts millions of visitors each year.

1.7 Billion Years Ago

Precambrian Era. Oldest metamorphic rocks (schist and gneiss) are formed.

Gneiss found in Rocky Mountain National Park

544-245 Million Years Ago

Paleozoic Period. Inland seas cover the north depositing thick layers of marine sediments that would later turn into sandstone and limestone

Geologic sediment deposit in Palezoic period

285 Million Years Ago

Ancient Rockies are formed. Very small mountain range only reaching up to 2,000 feet. Over the next couple hundred million years the Ancient Rockies eroded away, leaving behind sediment and less rugged landscape.

Ancient Rocky Mountains, before major erosion

200 Million Years Ago

Rocky Mountain National Park began to form after North American had broken from Pangea heading west. With its full force, North America slammed into a major micro continent with roots going deep into the crust. The collision of these two continents created a ripple effect that pushed granite (the basement rock) through layers upon layers of sedimentary rock sprouting up the Western Rockies. This collision happened again later, which made the Rockies even bigger.

Video of colliding tectonic plates in Pangea

As the mountains pushed up they were met with erosion that immediately started to tear them down. Erosion has scraped more than two miles of solid rock off the mountains. Reduced to low hills, the summits were only a few hundred feet high. The main source of erosion is water.

100 Million Years Ago

The entire state of Colorado was submerged under the Western Interior Seaway. Flooding left behind large sediment deposits, such as Pierre Shale and Fox Hills Formation (sandstone).

Map of the Western Interior Seaway. Colorado including the eroded Rocky Mountains were completely underwater.

75 Million Years Ago

Laramide Orogeny (mountain-building event) began. This process uplifted the modern Rocky Mountains. The Kula and Farallon Plates were subducting at a shallow angle under the North American Plate, lifting the Rocky Mountains to the height they are today. This process was followed by volcanic ash falls and mudflows, which left behind igneous rocks.

Subduction of the Oceanic Crust benath the

Continental Crust caused the Laramide Orogeny

66 to 2.6 Million Years Ago

Tertiary Period. Another period of uplift and erosion raised the Rockies to their current height and removed significant amounts of sedimentary deposits and revealed much older basement rocks from the Precambrian Era.

Ancient Schist found in Rocky Mountain National Park

300,000 to 127,000 Years Ago and 30,000 to 12,000 Years Ago

Glaciation, the process of land being covered by ice sheets, is the cause of the modern shape of the mountains in Rocky Mountain National Park. There hae been at least six glaciation events within the last 700,000 years that have made significant alterations to the landscapes, creating some of the famous features of the park.

Glacial Striations indicate glaciers moving over rocks during a glaciation event

Today

Geologists are unsure how the Rockies have remained stable at their massive size throughout time. While yet to be proven, they believe it’s a combination of a very dense crust underneath the mountains and a hot underlying mantle supporting the weight. Additionally, The Rockies are a very unique mountain range because they are located far away from plate boundaries while most mountain ranges are formed fairly close to active tectonic boundaries. A true phenomenon!

Snow covered modern Rocky Mountain peak in Colorado

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