Geodiversity Atlas—Southern Plains Network Index

Photo of a hill slope with dark rock outcrops and low vegetation.
Basalt lava flows of the Capulin Basalt cover the landscape of Capulin Volcano National Monument, New Mexico. The summit of Capulin Volcano appears in the background of the photograph.

NPS photo.

Geology and Stratigraphy of the Southern Plains Network Parks

The Southern Plains Inventory & Monitoring Network consists of 12 national park units in southeastern Colorado, northeastern New Mexico, western Kansas, Oklahoma, and north and central Texas. These units are Alibates Flint Quarries National Monument, Bent’s Old Fort National Historic Site, Capulin Volcano National Monument, Chickasaw National Recreation Area, Fort Larned National Historic Site, Fort Union National Monument, Lake Meredith National Recreation Area, Lyndon B. Johnson National Historical Park, Pecos National Historical Park, Sand Creek Massacre National Historic Site, Waco Mammoth National Monument, and Washita Battlefield National Historic Site. The parks that comprise the Southern Plains Network protect a combined 32,596 hectares (80,548 acres) of wilderness and vary in size from 43 hectares (107 acres) in Waco Mammoth to 18,201 hectares (44,978 acres) in Lake Meredith.

Geographically, the southern Great Plains is an immense sweep of country that reaches from south-central Texas to the northern border of Kansas and spreads out east of the Rocky Mountains. There is often a misconception of the Great Plains as a drab, flat, featureless area, when in fact the region encompasses a suite of diverse geologic landscapes that include canyons carved into solid rock by the waters of the Pecos River, the seemingly endless grainfields of Kansas, the precipitous peaks of the Sangre de Cristo Mountains, and the volcanic terranes of New Mexico.

Most of the park units of the Southern Plains Network occupy one of several sections of the Great Plains physiographic province such as the Central Texas Uplift (Lyndon B. Johnson, Waco Mammoth), High Plains (Alibates Flint Quarries, Lake Meredith, Sand Creek Massacre), Pecos Valley (Pecos), Raton (Capulin Volcano, Fort Union), Colorado Piedmont (Bent’s Old Fort), and Plains Border (Fort Larned). The Central Texas Uplift is a forested prominence at the southern end of the Great Plains. The High Plains is characterized by an expansive, nearly flat plateau that extends from the Texas Panhandle north to Nebraska and forms the central backbone of the Great Plains. The South Platte and Arkansas Rivers and their tributaries have dissected an area along the Rocky Mountain front that is called the Colorado Piedmont. The Pecos Valley section is a broad excavated valley of the Pecos River that stretches southward from the Sangre de Cristo Mountains in New Mexico into Texas. Green, crop-filled valleys with gently sloping valley walls and rounded stream divides trend eastward from the High Plains of western Kansas and characterize the Plains Border section (Trimble 1980). Situated between the Colorado Piedmont on the north and the Pecos Valley on the south are the volcanic vents, cinder cones, and lava fields that define the distinctive Raton section.

The mountainous sections of the southern Great Plains were formed long before the remaining areas were outlined by erosion. One of the oldest structural features is the Llano Uplift, which represents the crystalline core of a mountain belt produced during the Precambrian. Basement uplifts such as the Arbuckle and Amarillo were formed around the Pennsylvanian–Permian during the final collisional stages that resulted in the supercontinent Pangea. The Central Texas Uplift began as the continental interior was raised and the last Cretaceous inland sea retreated approximately 70 million to 65 million years ago. These regions stood well above the surrounding plains long before any sediments from the distant Rocky Mountains began to accumulate at their bases (Trimble 1980).

In southern Colorado and northern New Mexico, molten rock (magma) was emplaced into older Precambrian basement rocks and Paleozoic and Mesozoic sedimentary strata during the Oligocene (~29 million and 22 million years ago), leading to widespread volcanic eruptions. Another pulse of intermittent volcanism began about 9 million years ago during the Miocene, with eruptions as young as 37 thousand years ago associated with the Raton-Clayton volcanic field (Capulin Volcano) and Ocaté volcanic field (Fort Union). A thick sequence of basalt flows accumulated at Raton Mesa and Mesa de Maya between 8 million and 2 million years ago. The archetype cinder cone of Capulin Volcano was created by a violent eruption during the Pleistocene only 54,000 years ago (Trimble 1980; KellerLynn 2015a). Many of these volcanic masses were present before major downcutting by streams began, which provided huge quantities of sediment that were subsequently transported to the plains and deposited. Regional uplifts that occurred between 10 and 5 million years ago enhanced stream incision that sculpted the modern landscape of the Colorado Piedmont, Pecos Valley, and 13 Plains Border sections. Many of the individual landforms of the southern Great Plains that now attract the eye have been created by geologic processes during the last 2 million years (Trimble 1980).

A Brief Geologic History—Southern Plains Network

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

Cenozoic strata are mapped in every park unit of the Southern Plains Network, with formally named units that include the Neogene Ogallala Formation in Alibates Flint Quarries/Lake Meredith, Pleistocene Broadway Alluvium in Bent’s Old Fort, and the Pleistocene Capulin Basalt in, Capulin Volcano. Geologically young, Quaternary-age surficial deposits include alluvium (Bent’s Old Fort, Chickasaw, Fort Larned, Fort Union, Lake Meredith, Lyndon B. Johnson, Pecos, Sand Creek Massacre, Waco Mammoth), colluvium (Chickasaw, Pecos), fluvial river terraces (Alibates Flint Quarries/Lake Meredith, Pecos, Washita Battlefield, Waco Mammoth), terrace valley fill (Fort Larned), floodplain deposits (Washita Battlefield), loess (Fort Larned), and eolian sand deposits or paleodunes (Lake Meredith, Sand Creek Massacre, Washita Battlefield).
Rocks of the Mesozoic Era form the bedrock of six park units of the Southern Plains Network. Triassic-age strata of the Tecovas and Trujillo Formations are found in southern Lake Meredith, and Triassic rocks of the Moenkopi, Santa Rosa, and Chinle Formations are found in the Cañoncito subunit at Pecos. The Cretaceous Period is represented by the Greenhorn Limestone in Bent’s Old Fort, Graneros Shale in Fort Union, Shingle Hills Formation in Lyndon B. Johnson, and the Niobrara Formation in Sand Creek Massacre.
Paleozoic strata are mapped in nearly half of the park units of the Southern Plains Network, with some of the oldest exposures represented by the Cambrian Wilberns Formation in Lyndon B. Johnson National Historical Park. A thick sequence of Ordovician rocks occurs in Chickasaw and includes the Simpson Group (Joins, Oil Creek, McLish, Tulip Creek, and Bromide Formations), Viola Group, and Sylvan Shale. These are followed by the Silurian–Devonian Hunton Group (Cochrane, Clarita, Henryhouse, Haragan, and Bois d’Arc Formations). The later Devonian is represented by the Woodford Shale in Chickasaw. Mississippian sedimentary rocks also underlie Chickasaw and consist of the Sycamore Limestone, Caney Shale, and Springer Formation. Pennsylvanian strata are mapped in two park units of the Southern Plains Network and include the Deese Group, Collings Ranch Conglomerate, and Vanoss Formation in Chickasaw, as well as the Alamitos and Sangre de Cristo Formations at Pecos. Rocks of the Permian Period are represented by the Alibates Dolomite and Quartermaster Formation in Alibates Flint Quarries/Lake Meredith, the Yeso Formation, Glorieta Sandstone, San Andres Formation, and Artesia Formation in Pecos, and the Cloud Chief and Doxey Formations in Washita
Battlefield.
Precambrian basement rocks are found in only one park of the Southern Plains Network, underlying the western portion of the Cañoncito subunit in Pecos. These ancient igneous and metamorphic rocks date to the Paleoproterozoic Era (2.5 to 1.6 billion years ago) and consist of granite to granitic gneiss.

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    Type Sections—Southern Plains 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: Southern Plains 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.

    • Alibates Flint Quarries National Monument, Texas [Site Under Development]

    • Bent’s Old Fort National Historic Site, Colorado (no designated stratotypes identified)

    • Capulin Volcano National Monument, New Mexico [Site Under Development]

    • Chickasaw National Recreation Area, Oklahoma (no designated stratotypes identified)

    • Fort Larned National Historic Site, Kansas (no designated stratotypes identified)

    • Fort Union National Monument, New Mexico (no designated stratotypes identified)

    • Lake Meredith National Recreation Area, Texas (no designated stratotypes identified)

    • Lyndon B. Johnson National Historical Park, Texas (no designated stratotypes identified)

    • Pecos National Historical Park, New Mexico (no designated stratotypes identified)

    • Sand Creek Massacre National Historic Site, Colorado (no designated stratotypes identified)

    • Waco Mammoth National Monument, Texas (no designated stratotypes identified)

    • Washita Battlefield National Historic Site, Oklahoma (no designated stratotypes identified)

    The full Network report is available in digital format from:

    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

    Last updated: August 25, 2023

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