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Rocky Mountain National Park

Geologic Setting

Looking west from Denver the Front Range rises from the plains in two giant steps: first the foothills that climb above the “Mile High City,” then the high alpine summits, 54 of which loom above 14,000 feet (4,267 m). The difference in elevation between the peaks and nearby lowlands is striking. The square- topped silhouette of Longs Peak (14,256 ft, 4,345 m), the highest mountain in Rocky Mountain National Park, is the northernmost “fourteener” (mountains that exceed 14,000 feet above sea level) and towers 9,000 feet (2,743 m) above the adjacent plain. Longs Peak, a mass of Precambrian Silver Plume Granite, has challenged climbers since 1868 when a small party, that included John Wesley Powell, made the first recorded ascent. The infamous Diamond of Longs Peak, which ranks as the largest, highest, and steepest wall in the Southern Rockies, remains alluring to technical rock climbers from around the world.

The high country of the park consists of mountain peaks ranging in elevation from 11,000 to 14,000 feet (3,350 to 4,270 m) above sea level that form the Continental Divide, Trail Ridge, the Mummy Range, and the Never Summer Mountains. In addition to their height, the age of the rocks that form the core of these mountains is impressive. Although not the oldest rock in the National Park System (Grand Teton National Park holds that honor), they are from the same geologic time span, the Precambrian, which contains the oldest rocks on Earth and harkens back to a time when Earth’s early crust and continents were forming. Volcanism formed much younger rocks (23 to 29 million years ago), which lie on the western slope of the park and constitute much of the Never Summer Mountains.

Much of the high country consists of gently rolling topography into which glaciers have cut cirques and valleys. Although the rocks that comprise the range are ancient, the timing of its uplift makes the Southern Rockies geologic newcomers as compared to mountain ranges such as the Appalachians. Like the ranges that were here before them, the Rockies began their rise from the bed of an ancient sea, but in this case just 70 million years ago during a period of mountain building called the Laramide orogeny. The north- south trending Front Range is principally the result of Laramide mountain building, faulting, and subsequent erosion. Present- day relief was enhanced by additional uplift during Cenozoic time (the most recent geologic era).

The Front Range contains some of the most accessible alpine scenery in the Southern Rockies. Rocky Mountain National Park preserves thousands of acres of mountain meadows, snow- fed streams, rolling alpine uplands, glacial moraines and valleys, volcanoes, lava, and ash. Trail Ridge Road traverses 50 miles (80 km) of rugged, mountain terrain between the resort communities of Estes Park and Grand Lake. The 11- mile (18- km) section of road that lies above tree line follows the Continental Divide and winds through periglacial environments covered by alpine tundra. More than 300 miles (483 km) of hiking trails provide access from roadways and trailheads to remote areas of the park.

Rocks and deposits are the foundation of today’s scenery and record the geologic history and evolution of the park, which spans nearly two billion years. The evolution of the park’s landscape may be highlighted with these geologic events:

Precambrian Time

• Sediment deposited in an ancient sea (1,800 to 2,000
million years ago)
• Sedimentary and volcanic rocks metamorphosed into
biotite schist and biotite gneiss (1,750 million years ago)
• Intrusion of Boulder Creek Granordiorite (1,664
million years ago)
• Intrusion of granitic batholiths: Hagues Peak Granite
(1,480 million years ago) and Silver Plume Granite
(1,420 million years ago)
• Intrusion of the Iron Dike (1,317 million years ago)
• Erosion of mountains (1,300 to 500 million years ago)

Paleozoic and Mesozoic Eras

• Shallow sea covered the area (500 to 300 million years
• Accumulation of marine sediments on beveled
Precambrian mountains
• Intrusion of kimberlites (probably during the
Devonian Period, 417 to 354 million years ago)
• Formation of the Ancestral Rocky Mountains (300
million years ago) and erosion of pre- Mississippianage
• Intermittent inundation by seas (Permian to
Cretaceous, 286 to 65 million years ago)
• Deposition of marine, fluvial, and aeolian deposits
• Beginning of Laramide orogeny (70 million years ago,
Late Cretaceous)
• Withdrawal of seas

Cenozoic Era

• Laramide orogeny continues (including uplift, volcanism, erosion, fluvial deposition)
• Ongoing erosion (Mesozoic strata stripped away, exposing Precambrian rocks)
• Intrusion of granitic magmas and eruption of lava flows and ash (29 to 23 million years ago)
• Continued erosion; uplift, broad up- arching, and block faulting
• Canyon cutting (continues to present)
• Global climate cooling (beginning timing unknown, possibly about 2.5–2.6 million years ago; major climatic cooling by 800,000 years ago)
• Glaciation: Bull Lake (beginning timing unknown to about 127,000 years ago) and Pinedale (beginning about 30,000 years ago; glacial maximum between 23,500 and 20,000 years ago; 15,000 and 12,000 years ago deglaciation occurred; prior to 10,000 years ago, all Pinedale glaciers disappeared)
• Neoglaciation (about 5,000 to 120 years ago)
•Geomorphic processes continue to affect the present landscape

updated on 08/09/2007  I   http://www.nature.nps.gov/geology/parks/romo/geol_setting.cfm   I  Email: Webmaster
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