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Rocky Mountain

National Park


cover of park brochure

park geology subheading
frozen river
Rocky Mountain National Park, Colorado

The grandeur of Rocky Mountain National Park is the culmination of many geologic events:

  • the formation of the rocks through hundreds of millions of years,

  • the repeated uplift of the mountains by gigantic tectonic forces, and

  • millions of years of erosion by water and ice that sculpted the mountains into their present forms.

Brief geologic history
Most of the rocks in Rocky Mountain National Park—excluding the newer rocks of the Never Summer Mountains—originally were shale, siltstone, and sandstone, along with some volcanic rocks deposited about 1.8 to 2 billion years ago in an ancient sea. Between 1.7 and 1.6 billion years ago, these sedimentary rocks were caught in a collision zone between sections of the Earth's crust called tectonic plates.

These rocks, then in the core of an ancient Proterozoic mountain range, were recrystallized into metamorphic rocks by enormous heat and pressure resulting from the collision. The shale, which contained mostly clay minerals and some very fine sand and silt, was converted into biotite schist. The layers with more sandstone were converted into biotite gneiss.

Granites found in the park probably resulted from the melting of pre-existing sedimentary or metamorphic rocks in the primordial crust shortly after the formation of the Earth. The Silver Plume granite that occurs in much of the east side of the park intruded upward into the metamorphic rocks about 300 million years after the formation of the Proterozoic mountains. We do not know what caused this igneous episode.

The high mountains that formed here during Proterozoic time were slowly eroded and reduced to a fairly flat surface, exposing the core of metamorphic rocks and granite. This erosion occurred over a long period, from approximately 1,300 million to 500 million years ago. Little else is known about the geologic events in this area during this time span because no rocks of that age are present in the region.

About 500 million years ago, this relatively flat area became covered with shallow seas. Over the next 200 million years, several hundreds of thousands of feet of Paleozoic sedimentary rocks were deposited on the old Proterozoic surface. During the middle Pennsylvanian Period, yet another mountain range was uplifted in this area. From it the Paleozoic Period sediments were eroded.

Sediments shed from these "ancestral Rocky Mountains" were deposited along the mountain flanks. Today, these make up the Fountain Formation, which comprises the

  • "Flatirons" west of Boulder, Colorado;
  • the spectacular walls of Red Rocks Park west of Denver; and
  • the red rocks in the Garden of the Gods near Colorado Springs.
The Fountain Formation appears as a fairly continuous outcrop along the east edge of the present mountain front.

The area that is now Rocky Mountain National Park was eroded again and intermittently covered by seas from the middle of the Permian Period to the end of the Cretaceous Period about 65 million years ago. Abundant bones and tracks found in sedimentary rocks in the Rocky Mountain region date back to Jurassic and Cretaceous times, indicating that dinosaurs lived here during those periods.

Major tectonic plates of the Earth's crust began to collide along what was then the western edge of North America about 130 million years ago. Uplift caused by this collision began to affect the area of the present Colorado Rockies about 70 million years ago. As the region began to rise, the Cretaceous sea withdrew and the thick layer of sedimentary rocks that had accumulated began to erode. Within a few million years, the sedimentary rocks of the Front Range had eroded away, and the Proterozoic igneous and metamorphic rocks again were exposed to erosion.

As uplift proceeded, deep fault zones formed as enormous stresses pulled the Earth's crust apart at what is now the west side of the park. This allowed granitic magmas to rise into the present area of the Never Summer Mountains. Between 29 and 24 million years ago, the magmas reached the surface and erupted as volcanoes. The tops of the volcanoes stood several thousand feet above the present granitic masses of the Never Summers, which since have been eroded to their present size. Lava flows and extensive ash beds from the volcanoes are preserved in several areas within the park.

valleys and ridges created by glaciers
Landforms such as valleys and ridges are the result of the previous glaciation of Rocky Mountain National Park.

From the plate collision to the present, rivers and streams have eroded the mountains and transported enormous amounts of sediment to the oceans. By the end of the Tertiary Period, the mountains of Rocky National Park were still fairly high but rounded. The area also was characterized by wide, V-shaped stream valleys.

Then, the Rocky Mountain National Park area saw more drama. About 2 million years ago, Earth's climate cooled and the Ice Age began. Large ice sheets ebbed and flowed across much of the Northern Hemisphere. During several major periods of glaciation—as well as several minor episodes—ice covered much of North America and Europe. The high mountain valleys filled with glaciers.

Rocky Mountain National Park felt the effects of the Ice Age. Glaciation in the park probably started about 1.6 million years ago. Specific evidence of the earliest glaciations doesn't exist because moraines formed by the early glaciers were destroyed by glaciers that followed later. Each time glaciers flowed down the mountain valleys they eroded the valley sides and bottoms, helping to straighten and deepen them, removing evidence of earlier glaciations.

Evidence of the last two major periods of ice accumulation is quite clear, however. The first of these two glacial periods is called the Bull Lake Glaciation. The Bull Lake advance began about 300,000 years ago and ended about 130,000 years ago. A few isolated remnants of moraines from the Bull Lake glaciers can be identified at various places in the park. They indicate that the amount of ice in the valleys then was equal to or greater than ice volume during the most recent period of glaciation.

After the Bull Lake glaciation came a warmer period that lasted about 100,000 years. The last major glacial episode, called the Pinedale Glaciation, began about 30,000 years ago when Earth's climate once again cooled. The Pinedale glaciers reached their maximum extent between 23,500 and 21,000 years ago. Most of the major valleys in the park were filled with glaciers during this time. One of the largest of the park glaciers, with a length of 13 miles (21 km), was in Forest Canyon just south of the high point of today's Trail Ridge Road. The largest glacier, about 20 miles (52 km) long, was the ice flow that occupied the Colorado River Valley on the west side of the park. The ice in many of these glaciers reached thicknesses of 1,000 to 1,500 feet (305 to 457 m).

historic photo of Longs Peak

The Chasm and Mills moraine of Longs Peak as seen from the east atop Twin Sisters. By Photographer: T. W. Lee in 1916.

Between 15,000 and 12,000 years ago, the climate warmed and the glaciers rapidly disappeared. The only glaciers found in the park today occupy locations that receive a large amount of snow blown across the mountain ridges into northeast-facing, shaded cirques where snow melts slowly during summer. None of these glaciers are remnants of Ice Age glaciers.

Some scientists believe that we are living today in a warming interglacial period. But they speculate that climates might cool again, and the glaciers could return.

Points of Geologic Interest

Longs Peak is the highest peak in the park, cresting at 14,255 ft with a conspicuous flat summit. It is a prominent feature from many vantage points along roads in the park, and along many backcountry hiking trails. South of Estes Park on Highway 7, a roadside viewing area provides a fine view of the northeast face, a 1,000-foot sheer cliff of the glacial cirque headwall called The Diamond.

Trail Ridge Road takes visitors on a traverse back in time over the park's high mountain ridges. Here are remnants of the most ancient rocks in the park, recognizable by the marbled gray, white, and black bands of minerals in granular streaky gneiss and the darker, finer grained schist. The Silver Plume Granite is distinctive for its gray-tan and pink-red coloration and for the prominent feldspar crystals that sparkle in the sunlight.

visitors enjoying accessible geology
Visitors enjoying the accessible geology near Trail Ridge Road.
Horseshoe Park is named for the glacial moraines that rim the valley in the shape of a horseshoe. A giant alluvial fan that spreads into the upper end of Horseshoe Park marks the catastrophic discharge from the failed Lawn Lake Dam on July 15, 1982, which sent a torrent of water and huge boulders down the Roaring Fork River to the valley floor.

Old Fall River Road is a one-way road from Endovalley to the Alpine Visitor Center. It crosses Chiquita Creek, where there is a good view of Hanging Valley. Geologists believe that this canyon and the Fall River Canyon were once on the same level. However, the carving action of the Fall River Glacier scraped the main gorge so deeply that the side canyon was left hanging high up on the wall. Across the creek, you can see pits in granite rock, ground out by the swirling waters of the glacier.

Glacier Gorge has one of the park's best examples of a classic glacier-carved, U-shaped valley, which is visible from Bear Lake and Fall River Valley. The sharp peak of The Spearhead in Glacier Gorge is a “horn”, a pyramidal spire that remains after glaciers carved cirques on three or more faces of the peak.

Moraine Park's long, wooded slope at its south edge is a classic example of the lateral moraine, rock rubble that forms at the side of a glacier. Close examination of the moraines along both north and south flanks of Moraine Park show deposits of the older Bull Lake Glaciation and the younger, more prominent Pinedale Glaciation.

Kawuneeche Valley is a long, broad glacial valley formed by water and ice erosion along a major fault zone. Looking south from Farview Curve, you can see the headwaters of the Colorado River (originally named the Grand River) meandering along it. Over the past several hundred thousand years, the valley has been widened and its walls steepened by several glaciers fed from the Never Summer Mountains across the valley and from the Milner Pass area. The Colorado gathers strength and flow volume here from snow melt before descending through Glenwood Canyon in Colorado, the former Glen Canyon in Arizona, and ultimately, the Grand Canyon to the Gulf of California.

Grand Ditch is a water diversion project located alongside the Never Summer Mountains that predates the establishment of Rocky Mountain National Park. Construction was begun in 1890 and completed in 1936. The 17 mi system delivers an average of 20,000 acre-feet of water annually over the Continental Divide at La Poudre Pass to the eastern plains of Colorado.

The Never Summer Mountains are in large part are roots of extinct volcanoes. Several thousand feet of volcanic rock eroded away; what remains today is granitic rock that are the remnants of the magma chambers below the volcanoes that erupted between 24 and 29 million years ago.

Numerous mining claims were staked in the late 1800s in the Never Summer Mountains (and elsewhere in the park). One of these sites is Lulu City (about 3 miles up the Colorado River Trail). Optimistic prospectors hoped for silver and gold. Rocky Mountain National Park’s location just beyond the Colorado Mineral Belt-- which produces gold, silver, tungsten, molybdenum, uranium, lead, and zinc-- obviously disappointed those prospectors but made possible the setting aside of this area as a national park that has no minerals of commercial value.

old cabin
Remains from a previous era.

Geologic History
Ancient rocks form the core of the mountains in Rocky Mountain National Park. These rocks are more than 1,700 million years old and are from Precambrian time. In areas less exposed to the forces of heat and . . . read more

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 . . . read more

Geologic Features & Processes
The Colorado River originates in Kawuneeche Valley in Rocky Mountain National Park. Here it is very narrow, contrasting greatly with the segment of the river that flows through Grand Canyon National Park. The river flows 1,400 miles (2,253 km) from its birthplace in the park . . . read more

Full Report: cover of scoping report

Geologic Resource Evaluation Report – A detailed geologic report is available that provides an introduction to the geologic history of the park and its geologic formations, identifies geologic features and processes that are important to park ecosystems, describes key resource management challenges and possible solutions, and lists geologic research and monitoring needs.


park maps subheading

The General park map handed out at the visitor center is available on the park's map webpage.

For information about topographic maps, geologic maps, and geologic data sets, please see the geologic maps page.

photo album subheading

A general photo album for this park can be found here.

For information on other photo collections featuring National Park geology, please see the Image Sources page.

books, videos, cds subheading

Currently, we do not have a listing for a park-specific geoscience book. The park's geology may be described in regional or state geology texts.

Please visit the Geology Books and Media webpage for additional sources such as text books, theme books, CD ROMs, and technical reports.

Parks and Plates: The Geology of Our National Parks, Monuments & Seashores.
Lillie, Robert J., 2005.
W.W. Norton and Company.
ISBN 0-393-92407-6
9" x 10.75", paperback, 550 pages, full color throughout

The spectacular geology in our national parks provides the answers to many questions about the Earth. The answers can be appreciated through plate tectonics, an exciting way to understand the ongoing natural processes that sculpt our landscape. Parks and Plates is a visual and scientific voyage of discovery!

Ordering from your National Park Cooperative Associations' bookstores helps to support programs in the parks. Please visit the bookstore locator for park books and much more.

geologic research subheading

Research and management studies have been conducted at Rocky Mountain National Park for decades, but they have become essential tools as challenges facing management of the Park have increased. Rocky Mountain National Park, for all its grand beauty and sense of wildness, is embedded in a human environment that creates special challenges. Nitrogen deposition, growing elk populations, and fragile ecosystems are major management concerns. Growing numbers of visitors come to Rocky Mountain National Park every year, 2002 visitor numbers about 3.3 million. Each of those visitors has different expectations, both for the wildland experience he or she desires and the ammenities he or she needs. Further, the Park was established not only to serve today's visitors, but to serve visitors in generations to come whose expectations we can only surmise. Managers need the best scientific information available to juggle these many conflicting interests.

Information about the park's research program is available on the park's research webpage.

For information about permits that are required for conducting geologic research activities in National Parks, see the Permits Information page.

The NPS maintains a searchable data base of research needs that have been identified by parks.

A bibliography of geologic references is being prepared for each park through the Geologic Resources Evaluation Program (GRE). Please see the GRE website for more information and contacts.

selected links subheading

NPS Geology and Soils Partners

NRCS logoAssociation of American State Geologists
NRCS logoGeological Society of America
NRCS logoNatural Resource Conservation Service - Soils
USGS logo U.S. Geological Survey

teacher feature subheading

General information about the park's education and intrepretive programs is available on the park's education webpage.

For resources and information on teaching geology using National Park examples, see the Students & Teachers pages.
updated on 08/09/2007  I   http://nature.nps.gov/geology/parks/romo/index.cfm   I  Email: Webmaster
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