USGS2025
Introduction An Inventory of Stratigraphic Origins within the National Park Service The geologic history of Earth is recorded in layers or bodies of rock that are classified in a hierarchical order with several different categories of geologic units, including: supergroup, group, formation, member, bed, supersuite, suite, or complex. Geologists analyze and classify rock types based on properties that include lithology, texture, thickness, sedimentary structures, fossils, geographic or geospatial distribution, and age. In instances where new geologic units are proposed, a stratotype is assigned to a designated section, locality, or area of well-exposed rock that displays diagnostic characteristics for identification and correlation. Stratotypes are also namesakes, in that formally recognized rock units are named for the places where they were first described, measured, and mapped. Thus, a vast majority of the stratigraphic nomenclature alludes to geographic or geologic features. Some particularly recognizable examples (and their stratotype assignments) include the Paleoproterozoic Vishnu Schist (Vishnu Canyon in Grand Canyon National Park, Arizona), the Early Cambrian Harpers Formation (Harpers Ferry National Historical Park, West Virginia), and the Late Cretaceous Whitney Granodiorite (Mount Whitney in Sequoia and Kings Canyon National Parks, California). Beginning in 2020, the National Park Service (NPS) began a systematic effort to document the occurrence of stratotypes exposed within, partially within, and near NPS administrative boundaries. The NPS stratotype inventory project represents an important component of a geologic resource inventory, as these designations are vital to our national geologic heritage (herein referred to as “geoheritage”) and possess significant scientific, historic, educational, cultural, and aesthetic values. The geoheritage significance of stratotypes is analogous to libraries and museums, in that they are geologic landmarks of Earth history and record the prodigious forces and evolving life forms that define our understanding of the planet. These designated exposures preserve knowledge, represent comparative geologic references where previous observations can be re-examined or reinterpreted, and can serve as valuable educational tools for future geoscientists (Brocx and others, 2019). The NPS stratotype inventory includes the following: Documentation of designated stratotype exposures to confirm their geospatial occurrence within, partially within, and near NPS administrative boundaries, compiled from published reports and maps; Compilation and visualization of the precise geographic locations of the stratotype exposures; and Recommendations that address potential land and resource management issues associated with NPS stratotypes. By achieving these goals, this project helps to raise awareness of stratotypes as a geologic resource by educating NPS staff and the public so that they may better understand, recognize, and protect these important park resources. The focused approach adopted for conducting the stratotype inventories throughout the NPS has centered on the 32 Inventory and Monitoring (I&M) networks established by the NPS during the late 1990s (for more information on each network, see https://www.nps.gov/im/networks.htm). The I&M networks represent groups or clusters of park units that are based on shared geography and natural resource characteristics. The Greater Yellowstone I&M Network, encompassing Bighorn Canyon National Recreation Area, Grand Teton National Park, John D. Rockefeller Jr. Memorial Parkway, and Yellowstone National Park, was used as the pilot network for initiating this stratotype inventory and was first published in November 2020 (Henderson and others, 2020). The 32d and final report on the Northeast Temperate I&M Network was published in October 2022 (Henderson and others, 2022). Currently, the NPS stratotype inventory project has identified more than 700 stratotypes within NPS administrative boundaries.