NPS Geodiversity Atlas—Lake Meredith National Recreation Area, Texas (U.S. National Park Service)

Geodiversity refers to the full variety of natural geologic (rocks, minerals, sediments, fossils, landforms, and physical processes) and soil resources and processes that occur in the park. A product of the Geologic Resources Inventory, the NPS Geodiversity Atlas delivers information in support of education, Geoconservation, and integrated management of living (biotic) and non-living (abiotic) components of the ecosystem.

image of lake meredith gri report cover with park landscape image — In-depth geologic information is contained in the baseline inventory products of the Geologic Resources Inventory, see table below.

Introduction

Lake Meredith National Recreation Area and the adjoining Alibates Flint Quarries National Monument (NM) are situated within a surprising section of canyon landscape below the Caprock Escarpment on the otherwise mostly flat High Plains of Texas. The Canadian River valley, also known as the Canadian Breaks, is the setting for Lake Meredith, the reservoir formed by the Sanford Dam. Lake waters lap up against red hillsides dotted with white boulders that have tumbled down the slopes. A series of red-rock side canyons and deposits of the colorful Alibates flint complete the Lake Meredith geologic tableau, resulting in one of the most scenic areas in the Texas Panhandle.

The Canadian Breaks region is characterized by a rolling landscape with low mesas, buttes and hills. Lake Meredith NRA was originally established in 1965 as Sanford National Recreation Area. At 44,978 acres in size, Lake Meredith NRA is best known for the fishing, boating, camping, hunting and hiking it offers. But it also provides one of the best windows into the geologic history and landscape evolution of the High Plains.

Geologic Features and Processes

Geologic features and processes identified in the park’s Geologic Resource Inventory include:

Geologic Structures
Permian Red Beds
Alibates Dolomite and Alibates Flint
Triassic Rocks
Ogallala Formation
Paleontological Resources
Dissolution of Red Beds
Karst
Rock Shelter
Canadian River
Canadian Breaks and Caprock Escarpment
Lake Meredith
Aeolian Features and Processes

Geologic Setting

The Canadian Breaks are a major physiographic feature that cuts across the Texas Panhandle. Situated below the Caprock Escarpment, the transition point between the relatively flat plains and the canyon landscape of the Canadian River valley, the Canadian Breaks divide the High Plains physiographic province into the Central High Plains to the north from the Southern High Plains. The Caprock Escarpment is a widespread erosional scarp topped by caliche zone in the upper part of the Ogallala Formation, which is as thick as 30 ft (9 m).

Older geologic structures controlled the deposition of Permian and Triassic sedimentary rocks exposed in Lake Meredith NRA. The recreation area is located on top of the Amarillo uplift, a structural high between the Anadarko and Palo Duro basins. The Amarillo uplift is a buried mountain range that developed approximately 300 million years ago. The Amarillo uplift is buried by as much as 6,000 ft (1,800 m) of sediment and the Anadarko Basin, one of the deepest basins in the continental United States; is filled with approximately 40,000 ft (12,000 m) of sedimentary rock. The Palo Duro Basin contains about 10,000 ft (3,000 m) of sediment.

Geologic History

Most of the colorful red and white rock layers (formations) exposed in Lake Meredith NRA were deposited approximately 260 million years ago during the Permian Period when what is now the Texas Panhandle was located near the equator and was part of the supercontinent Pangaea.

These sandstones, siltstones and mudstones, along with interbedded layers of gypsum and dolomite, are collectively known as Permian red beds for their age and predominate red to orange hues. The Permian red beds were deposited near the margin of an arm of the sea that extended up from the south. Some of these sediments were deposited on coastal plains, others in marine basins and yet others in tidal flats. Massive amounts of salt and other evaporite minerals were included in these sediments that reach thousands of feet in thickness, mostly in the subsurface, with the greatest thickness south of the Lake Meredith region.

The Permian reds beds in Lake Meredith NRA were mapped as an undivided unit that consists of three different formations, identified as the Whitehorse Sandstone, Cloud Chief Gypsum, and Quartermaster Formation. These formations are difficult to distinguish except by stratigraphic position, but at Lake Meredith, stratigraphic markers are missing. Further, the nomenclature of Permian rocks in the Texas panhandle has a confusing history, making stratigraphic assignments complicated.

Red beds are colored by small amounts of iron oxides and clay minerals in them. The soft sandstones, siltstones and mudstones are easily eroded, making true outcrops of these rocks scarce. Instead, these rocks yield the rounded hills that make up much of the landscape in the Lake Meredith area.

The Alibates Dolomite is one of the few easily recognizable strata within the red bed sequence. The off-white unit is approximately 15 feet (4.5 m) thick. The Alibates consists of upper and lower dolomite layers with a middle red bed, but in many areas, the upper dolomite has been removed by erosion. The dolomite was deposited under hypersaline marine conditions such as in mud flat environments while the red beds were deposited in a terrestrial environment. In places, evidence of algae mats is preserved in the Alibates Dolomite.

In addition to being more resistant to erosion than the red beds and capping most of mesas and buttes adjacent to Lake Meredith, the Alibates Dolomite is also the source of Alibates flint, where it occurs as lenses or nodules in dolomite layers. Flint, also known as chert, consists of submicroscopic crystals of silica. The Alibates flint formed much later than the enclosing rock when silica replaced dolomite (calcium magnesium carbonate). The array of colors results from the presence of trace elements.

Alibates flint has been highly prized by American Indians for thousands of years for use in stone tools. More than 700 shallow pits or quarries are found in the area where native peoples burrowed for unfractured, unweathered chert for use in tool manufacture.

In most areas in and around the recreation area, the Tertiary Ogallala Formation directly overlies the Permian red beds, although Triassic sedimentary rocks are present in the southwestern part of the recreation area. The Triassic Tecovas and Trujillo formations are approximately 230-220 million years old and have been correlated to the famous Chinle Formation at Petrified Forest National Park in Arizona and throughout the American Southwest. These units were deposited in fluvial and alluvial environments.

The approximately 10-million-year-old Ogallala Formation is much younger than the underlying rocks, and sits atop a regional uncomformity, or period of missing time. The Ogallala Formation consists of materials shed from eroding mountainous areas to the west, and includes river, lake and wind deposits. The upper portion of the formation consists of caliche, a hardpan made up of calcium carbonate that forms in arid to semi-arid environments.

Landscape Evolution

After the deposition of the Ogallala Formation, the Canadian River carved its valley, which is as great as 40 miles (64 km) wide and 1,000 ft (300 m) deep, by incising into the caliche caprock within the last few million years. The Caprock Escarpment is the line of cliffs formed by the retreat of these cliffs through erosion into the canyons and broken country below.

The course of the Canadian River traces, at least in part, a broad zone of subsidence across the High Plains due to salt dissolution. Thick layers of salt and other evaporate minerals were precipitated in an enclosed arm of the sea prior to and at the same time that the red beds were deposited. Salt layers are susceptible to dissolution by groundwater and can cause collapse and subsidence of the overlying rock layers. The base of the Ogallala Formation in the collapse zone has subsided 300-600 ft (100-200 m) relative to other areas of the High Plains. The subsidence of the ground surface due to salt dissolution explains in part how the relatively small Canadian River carved such a large valley.

Much of the salt dissolution probably took place during the Pleistocene when the climate was significantly wetter. Subsurface salt dissolution is still occurring in the area as evidenced by the high saline levels in the Canadian River and the presence of sinkholes in the region.

Geologic Issues

The Permian and Pennsylvanian rocks in the Texas Panhandle are also host to oil and gas deposits, and a number of producing wells are located in and around Lake Meredith NRA. Oil and gas operations in the parks are administered by an oil and gas management plan.

Wind in the Texas Panhandle is constant. Wind erosion and dust storms can be significant geologic resource management issues at Lake Meredith NRA. During periods of drought when the lake level is low, large areas of the lake basin may be exposed to wind erosion. Areas of ORV use and oil and gas operations are also particularly susceptible to wind erosion. Vehicular traffic and creation of access roads denude vegetation, exposing the ground surface to wind erosion. Furthermore, vehicles churn up and transport dust, referred to as placed mats to reduce the amount of material available for windblown transport (KellerLynn 2011; see “Oil and Gas Production” section).

Lake Meredith

The Canadian River flows 906 mi (1,458 km) from the Sangre de Cristo Mountains in southern Colorado to a confluence with the Arkansas River in eastern Oklahoma.

The Lake Meredith was created by the construction of Sanford Dam on the Canadian River at a narrow point in the Canadian Breaks. Canadian River Municipal Water Authority manages the water of Lake Meredith, operating the the dam and managing water supply for 11 municipalities. Lake level fluctuates on account of municipal water demands, rainfall in the watershed, and releases from upstream reservoirs. The National Park Service is responsible for providing public access to recreational opportunities at Lake Meredith National Recreation Area, including water-based recreation in Lake Meredith and land-based recreation beyond the lake basin.

Cave and Karst

Most of Lake Meredith NRA is evaporative karst. Salt (halite) and gypsum in the Permian red beds are susceptible to dissolution by groundwater. Dissolution within Permian strata results in the collapse of overlying units. Collapse chimneys are distinctive dissolution-related features found in the recreation area. These chimneys are circular or elliptical in cross section and filled with collapse debris. Most chimneys are buried and only exposed in road cuts or bluffs, but some chimneys, stand in relief as the breccia infilling them are more resistant to erosion than the surrounding red beds.

Alcoves, or rock shelters, may form by softer strata eroding more rapidly and undercutting a harder layer above them. While these shallow depressions are not caves and were not formed by dissolution processes, they are protected as cavelike features under federal law.

All NPS cave resources are protected under the Federal Cave Resources Protection Act of 1988 (FCRPA)(16 U.S.C. § 4301 et seq.).

Paleontological Resources

While fossils have not been found in the Permian red beds, a variety of fossils have been documented in Lake Meredith NRA. The Alibates Dolomite contains layered algal mats or stromatolites. Algal mats form when algal filaments trap carbonate mud, usually in saline tidal flat environments. Petrified wood and bone fragments from reptiles and amphibians have been found Tecovas Formation in the Lake Meredith area. Reported fossils from the Ogallala Formation in or near Lake Meredith NRA include vertebrate, invertebrate and plant fossils.

Fossils, including part of a bison skull and a mammoth humerus, have been found in Quaternary sediments in Lake Meredith NRA. A deposit of the Lava Creek B ash, erupted from the Yellowstone caldera 639,000 years ago, contains crayfish burrows and abundant plant material.

All NPS fossil resources are protected under the Paleontological Resources Preservation Act of 2009 (Public Law 111-11, Title VI, Subtitle D; 16 U.S.C. §§ 470aaa - 470aaa-11).

Geohazards

Natural geologic processes continue to shape the recreation area on time scales ranging from seconds to years, and visitors should be cautious and alert to geohazards that may be present.

Mass wasting, including rockfalls, creep, slumps and topples may occur on the slopes in Lake Meredith NRA. Slope movements may occur on slopes made up of the Permian red beds, particularly below capstones made of the harder Alibates Dolomite. Boulders of the white Alibates Dolomite cascading down the red slopes of Lake Meredith NRA are one of the characteristic features of the park’s scenery. These boulders have fallen from the canyon rims and may travel further downslope.

Rotational slumping and rockfall occur on the slopes above the lake. Most of the slumps are on the northern side of Lake Meredith on south-facing slopes. When lake levels are high, wave action is a primary trigger in slumping.

Flash floods may occur in the many tributaries that flow into Lake Meredith, presenting a potential geohazard.

The Texas Panhandle has a relatively low seismic hazard. The USGS 2014 Seismic Hazard Map indicates that the Lake Meredith area has a 2% chance that an earthquake peak ground acceleration of between 10 and 14 %g (percent of gravity) being exceeded in 50 years due to natural earthquakes. Peak ground acceleration between 10 and 14 %g is roughly equivalent to VI on the Modified Mercalli Intensity Scale. The expected number of damaging earthquake shaking in the Texas Panhandle in 10,000 years is between 4 and 10.

Abandoned Mineral Lands

Two abandoned mineral lands (AML) sites, both former gravel pits used during construction of Sanford Dam, are present in Lake Meredith NRA. One site has been mitigated and the other site requires no mitigation.

NPS AML sites can be important cultural resources and habitat, but many pose risks to park visitors and wildlife, and degrade water quality, park landscapes, and physical and biological resources. Be safe near AML sites—Stay Out and Stay Alive!

Related Link

Burghardt, J. E., E. S. Norby, and H. S. Pranger, II. 2014. Abandoned mineral lands in the National Park System—comprehensive inventory and assessment. Natural Resource Technical Report NPS/NRSS/GRD/NRTR—2014/906. National Park Service, Fort Collins, Colorado.

Regional Geology

Lake Meredith National Recreation Area is a part of the Great Plains Physiographic Province and shares its geologic history and some characteristic geologic formations with a region that extends well beyond park boundaries.

Maps and Reports

The Geologic Resources Inventory produces digital geologic maps and reports for more than 270 natural resource parks. The products listed below are currently available for this park, check back often for updates as many maps, reports, and posters are still in progress.

Scoping summaries are records of scoping meetings where NPS staff and local geologists determined the park’s geologic mapping plan and what content should be included in the report.
Digital geologic maps include files for viewing in GIS software, a guide to using the data, and a document with ancillary map information. Newer products also include data viewable in Google Earth and online map services.
Reports use the maps to discuss the park’s setting and significance, notable geologic features and processes, geologic resource management issues, and geologic history.
Posters are a static view of the GIS data in PDF format. Newer posters include aerial imagery or shaded relief and other park information. They are also included with the reports.
Projects list basic information about the program and all products available for a park.

Source: Data Store Saved Search 3000. To search for additional information, visit the Data Store.

A NPS Soil Resources Inventory project has been completed for Lake Meredith National Recreation Area and can be found on the NPS Data Store.

Source: Data Store Saved Search 3047. To search for additional information, visit the Data Store.

rock outcrop overlooking park landscape — Alibates Dolomite is a distinctive layer in the Permian red beds at Alibates Flint Quarries National Monument. The dolomite yields the famous Alibates flint, which prehistoric peoples used for making tools. The dolomite also served as a “canvas” for prehistoric people to chip and peck petroglyphs.

NPS Geodiversity Atlas—Lake Meredith National Recreation Area, Texas

Introduction

Geologic Features and Processes

Geologic Setting