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. 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.
Series: National Park Service Geodiversity Atlas
NPS Geodiversity Atlas—Hot Springs National Park, Arkansas
Geologic Features and Processes
The park’s 47 hot springs are a mixture of older, thermal water and younger, shallow (cool) groundwater. Both are recharged from local precipitation. The thermal water is heated by Earth’s normal geothermal gradient, meaning there is no “hotspot” beneath Hot Springs. Geologic structures, including fractured bedrock, a plunging fold, and a thrust fault create the specific conditions that allow the water to be heated at depth and rise rapidly to the surface. Geologists are still investigating and delineating the recharge areas for both the thermal and cold water components.
Geologic structures control the development and flow of the thermal system at Hot Springs. These features formed during the intense compression associated with the Ouachita Orogeny. This part of the Ouachita Mountains contains fractured bedrock, as well as abundant, nearly parallel, overturned folds cut by thrust faults. The pattern of structures is complex. Differential erosion has caused softer shales to wear away more rapidly than harder sandstones, cherts, and novaculites. These resistant rocks (novaculite and sandstone) cap most of the ridges in the Zigzag Mountains.
In addition to the geologic framework being responsible for the emergence of hot springs, the area’s geology has long attracted interest in its mineral wealth. The novaculite and sandstone were used by American Indians beginning thousands of years ago. Novaculite use for whetstones continues today.
Marine invertebrate fossils have been discovered in the Ordovician, Silurian, Devonian, and Mississippian rocks delineated on the geologic map. Some plant and vertebrate fragments are noted from the Stanley Shale (Ms). Fossil graptolites are known from the park and are housed in the park’s museum collection.
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).
Geology Field Notes
Students and teachers of college-level (or AP) introductory geology or earth science teaching courses will find that each park's Geologic Resource Inventory report includes the Geologic History, Geologic Setting, and Geologic Features & Processes for the park which provides a useful summary of their overall geologic story. See Maps and Reports, below.
Hot Springs National Park is a part of the Ouachita Province and shares its geologic history and some characteristic geologic formations with a region that extends well beyond park boundaries.
Geologic Resources Inventory
- 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.
Hot Springs National Park
National Park Service Geodiversity AtlasThe servicewide Geodiversity Atlas provides information on geoheritge and geodiversity resources and values within the National Park System. This information supports science-based geoconservation and interpretation in the NPS, as well as STEM education in schools, museums, and field camps. The NPS Geologic Resources Division and many parks work with National and International geoconservation communities to ensure that NPS abiotic resources are managed using the highest standards and best practices available.
For more information on the NPS Geodiversity Atlas, contact us.