Geodiversity Atlas—Rocky Mountain Network Index

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Geology and Stratigraphy of the Rocky Mountain Network Parks

The Rocky Mountain Inventory and Monitoring Network consists of six parks located within the central and northern Rocky Mountain region of the United States in the states of Colorado and Montana. Glacier National Park is the northernmost of the network parks and lies along the U.S.–Canadian international border and incorporates the Lewis and Livingston ranges. Florissant Fossil Beds National Monument and Rocky Mountain National Park are associated with the Front Range in Colorado. Great Sand Dunes National Park and Preserve is part of the Sangre de Cristo Range, also in Colorado. The Continental Divide is a prominent feature which extends along the Rocky Mountain Cordillera within Glacier National Park and Rocky Mountain National Park. Florissant Fossil Beds National Monument, Great Sand Dunes National Park and Preserve, and Little Bighorn Battlefield National Monument all are located on the plains east of the Continental Divide, while Grant-Kohrs Ranch National Historic Site is located just west of the divide. The highest point of elevation in the Rocky Mountain I&M Network is 4,346 m (14,259 ft) above sea level on top of Longs Peak within Rocky Mountain National Park. The lowest point of elevation is 933 m (3,061 ft) above sea level at Little Bighorn Battlefield National Monument.

A Brief Geologic History—Rocky Mountain Network

A few examples of events and Network resources in each geologic time period are highlighted below, from youngest to oldest.

The Laramide Orogeny continued into the Cenozoic and further uplifted the Rocky Mountains into a chain of high-elevation mountain peaks and subsiding intermountain basins. Large volumes of rocks and sediments were eroded during and after this major mountain building event. The sediments, along with the products of periodic volcanism, accumulated in the intermountain basins and to the plains directly to the east. The Denver–Cheyenne and North Park sedimentary basins flank Rocky Mountain National Park and contain vast sediments shed from uplifted rock associated with the Laramide orogeny.

A transition from Laramide-related compression to Neogene extension led to the development of the Rio Grande Rift. The San Luis Basin contains Great Sand Dunes National Park and Preserve and is one the most dramatic grabens of the Rio 6 Grande Rift. The abrupt topographic relief along the active San Luis Basin boundary has effectively trapped the famous sands of the park where they remain today.

Eocene and Oligocene sedimentary and volcaniclastic units record the post-Laramide period in many of the Rocky Mountain Monitoring Network parks. These units include the Wall Mountain Tuff and the Florissant Formation at Florissant Fossil Beds National Monument, the Troublesome Formation and some igneous intrusives at Rocky Mountain National Park, the Renova Formation at e Grant-Kohrs Ranch National Historic Site, and the Kishenehn Formation at Glacier National Park. One of the world’s largest volcanic fields is the Oligocene-age San Juan volcanic field, located west of Great Sand Dunes National Park and Preserve. Detritus from the San Juan field is the main source of sand captured at the dunes.

During the Pleistocene, alpine and continental glaciation reshaped and modified the geomorphology and surficial features in the parks of the Rocky Mountain Monitoring Network. This Pleistocene and Holocene glacial activity was most pronounced at Glacier National Park and Rocky Mountain National Park and continues today, although greatly diminished due to the retreat and disappearance of some glaciers due to climate change.
The Mesozoic geologic record for the Rocky Mountain Monitoring Network parks is best represented by Upper Cretaceous marine and terrestrial sedimentary strata mapped in Little Bighorn Battlefield National Monument, Rocky Mountain National Park, and most extensively in Glacier National Park. The Cretaceous Interior Seaway influenced middle to late Cretaceous deposition in the area now represented by the Rocky Mountain Monitoring Network.

Beginning during the Late Cretaceous, approximately 75 million years ago, a mountain building event referred to as the Laramide Orogeny dramatically altered the landscape of western North America. A series of tectonic events resulted in the uplift and deformation of crust on the central craton with a corresponding retreat of the Interior Seaway. This orogenic event gave birth to the Rocky Mountains extending north to south from Canada into Mexico, and significantly reshaped the landscape of the Rocky Mountain Monitoring Network parks.
A long interval of erosion followed the igneous intrusive and metamorphic events of the Precambrian in the northern Rockies. This erosional period removed thousands of feet of rock, producing a major unconformity. Late Paleozoic mountain building during the Pennsylvanian (approximately 300 million years ago) formed the Ancestral Rocky Mountains, which were elevated along some of the faults in the crystalline Precambrian basement. Great Sand Dunes National Park and Preserve is situated just west of the ancestral Front Range (Apashapa block) within the central Colorado trough and contains sediments shed from the actively uplifted Sangre de Cristo Formation. The Paleozoic geologic record is preserved in only two of the Rocky Mountain Monitoring Network parks. Devonian igneous intrusive rocks are documented in Rocky Mountain National Park. More extensive Paleozoic strata are exposed at Great Sand Dunes National Park and Preserve, spanning from the Early Ordovician through the Permian.
Precambrian basement rocks are the foundation for the three Rocky Mountain Monitoring Network parks in Colorado. The Pikes Peak Granite (Mesoproterozoic) underlies the fossiliferous Eocene formations at Florissant Fossil Beds National Monument. Surrounding the intermountain basin of Great Sand Dunes National Park and Preserve are metamorphic gneiss (Paleoproterozoic) and intrusive igneous quartz monzonite (Paleoproterozoic and Mesoproterozoic) forming a barrier to the famous wind-blown sands accumulated into great 230 m (750 ft) high dunes. The alpine landscape of Rocky Mountain National Park is dominated by massive igneous and metamorphic complexes (Paleoproterozoic and Mesoproterozoic) with dozens of peaks standing above 3,657 m (12,000 ft) above sea level. One of the more notable Precambrian units in Rocky Mountain National Park is 5 the 1.664 billion-year-old Boulder Creek batholith. This massive igneous body was one of a series of intrusives which served as a heat source for regional metamorphism.

The most extensive Precambrian record is exposed in Glacier National Park. The Waterton Formation is the basement unit upon which lies a thick sequence of Mesoproterozoic formations recording a long geologic history, now uplifted by tectonics and cut by glaciers. The backbone of the northern Rocky Mountains is constructed of at least 13 Mesoproterozoic geologic formations, one of the most extensive Precambrian sequences in the NPS. Similar-aged, well-preserved and un-altered sections of old sedimentary rock are also exposed in the Grand Canyon.

Type Sections—Greater Yellowstone Network

thumbnail image of cover of type section report

The geologic history above is excerpted from a report titled, "National Park Service geologic type section inventory: Rocky Mountain Inventory & Monitoring Network". Type sections are essential reference locations for the geoscientists who study geologic history and paleontology. A summary of the type sections in each park can be found at the links below.

The full Network report is available in digital format from https://irma.nps.gov/DataStore/Reference/Profile/2283702

Please cite this publication as:

  • Henderson, T., V. L. Santucci, T. Connors, and J. S. Tweet. 2020. National Park Service geologic type section inventory: Rocky Mountain Inventory & Monitoring Network. Natural Resource Report NPS/ROMN/NRR—2020/2215. National Park Service, Fort Collins, Colorado.

NPS Stratotype Inventory

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