Geologic Type Section Inventory for Sierra Nevada Network Parks

Southern view across Evolution Lake, Kings Canyon National Park. Evolution Basin represents the type locality of the Evolution Basin Alaskite. At left of center is Mount Spencerk at right of center is the more distant Mount Huxley.

US Geological Survey

The NPS Geological Resources Division completed a report for Sierra Nevada Network parks that highlights geologic features (or “stratotypes”) of our parks that serve as the standard for identifying geologic units (Henderson et al. 2021). One example is Moro Rock in Sequoia National Park being a type locality for Giant Forest Granodiorite. There is a need to protect and monitor designated stratotypes, and there is also potential to nominate additional stratotypes in these parks.

Just as biologists use type specimens that provide a standard to define characteristics used in classification of plants and animals, geologists use type sections as a standard for recognizing and defining geologic units. Documentation of stratotypes (i.e., type sections/type localities/type areas) is a major portion of a geologic resource inventory. Stratotypes are important because they store knowledge, represent important comparative sites where past knowledge can be built up or re-examined, and can serve as teaching sites for the next generation of students. They can be thought of as a geoheritage, analogous to libraries and museums as they are natural sources of Earth history spanning ~4.5 billion years and record the forces and evolving life forms that define our planet.

But the existing documentation of geologic type sections in National Park Service areas has not been previously inventoried, and there is a general lack of baseline information for this geologic resource category. Also, NPS staff in parks may not be aware of the concept of geologic type sections or be aware of ones that may be identified or may yet need to be documented in their parks. The lack of awareness of the concept of geologic type sections leads to a lack of understanding of their significance or their occurrence in parks. Park staff well-informed about the existence and importance of geologic type sections will both be better able to monitor and protect them as well as share their value with partners and the public.

Please note: This article only shares highlights of the full published report – National Park Service Geologic Type Section Inventory: Sierra Nevada Inventory & Monitoring Network (Henderson et al. 2021). Please see that report (link in references below) for a more thorough discussion of Sierra Nevada Network park geology and type section inventory.

What stratotypes are designated in Sierra Nevada Network parks?

Devils Postpile National Monument

As of the writing of this report, there were no designated stratotypes identified within the boundaries of the monument. A list of 10 stratotypes located within 48 km (30 mi) of monument boundaries is included in the report for reference. These nearby stratotypes include the Triassic Scheelite Intrusive Suite (type area), Wheeler Crest Granodiorite (type locality), Cretaceous John Muir Intrusive Suite (type area), Lake Edison Granodiorite (type locality), Round Valley Peak Granodiorite (type locality), Mount Givens Granodiorite (reference locality), and Pleistocene Bishop Tuff (type locality), Tenaya Till (type locality), Till of Sherwin Glaciation (type locality), and Recess Peak Till (type locality).

Sequoia and Kings Canyon National Parks

The boundaries of SEKI contain 12 stratotypes that are associated with the formation of the Sierra Nevada batholith. These stratotypes are subdivided into eight type localities and four type areas (Figure 1). Stratotype units are:

• Mountain Whitney Intrusive Suite: Type area includes exposures along Sierra Nevada crest near Mount Whitney
• Whitney Granodiorite: Type Locality is approximately 200 m (660 ft) north of Mount Whitney summit
• Evolution Basin Alaskite: Type locality is exposures in Evolution Basin
• Lamarck Granodiorite: Type locality is cirques east of Mt. Larmarck
• Paradise Granodiorite: Type locality is on east side of Paradise Valley
• Mitchell Intrusive Suite: Type area is Tableland area, on divide between Kings and Kaweah Rivers
• Mitchell Peak Granodiorite: Type locality is Mitchell Peak
• Sequoia Intrusive Suite: Type area is exposures in Shell Mountain-Little Baldy area
• Giant Forest Granodiorite: Type locality is Moro Rock, just south of Giant Forest
• Inconsolable Quartz Monzodiorite: Type locality is Inconsolable Range
• Palisade Crest Intrusive: Type area is exposures along Palisade Crest, from east escarpment of Sierra Nevada south of Big Pine Creek to Red Mountain Creek
• Tinemaha Granodiorite: Type locality is in cirques at head of Tinemaha Creek

Figure 1. Modified geologic map of Sequoia and Kings Canyon National Parks showing stratotype locations. The transparency of the geologic units layer has been increased. (Henderson et al. 2021).

The oldest designated stratotype in these parks pertains to the Jurassic Tinemaha Granodiorite of the Palisade Crest Intrusive Suite. The granodiorite was named by Bateman (1961) after Mount Tinemaha, near the eastern border of Kings Canyon National Park. Type locality exposures are designated in the cirques at the head of Tinemaha Creek, in the cliffs of Mount Bolton Brown (Figure 1; Bateman 1961). Other notable exposures occur in the summits of Split Mountain, Mount Tinemaha, Birch Mountain, and The Thumb.

Yosemite National Park

Yosemite National Park contains two stratotype occurrences: one type locality and one type area (Figure 2). The oldest stratotype of the park pertains to the Early Cretaceous Fine Gold Intrusive Suite, the oldest formally named intrusive suite in the western Sierra Nevada, dated between 123–105 million years old (Bateman 1992). The Fine Gold Intrusive suite was named after exposures along Fine Gold Creek and consists of several igneous units. Bateman (1988, 1992) states that the type area is the Ward Mountain–Bass Lake area (Figure 2). A portion of the intrusive suite type area is located along the western boundary of Yosemite. The suite is characterized by granitoid bodies containing a low presence of alkali feldspar and 87Sr/86Sr (strontium isotope) ratios indicative of source magmas containing substantial amounts of crustal material (Bateman 1992). The Yosemite stratotype units are:

• Sentinel Granodiorite: Type locality is Sentinel Rock (Figure 3)

• Fine Gold Intrusive Suite: Type area is Ward Mountain-Bass Lake area, central Sierra Nevada

Figure 2. Modified geologic map of Yosemite National Park showing stratotype locations. The transparency of the geologic units layer has been increased. (Henderson et al. 2021)

Many geologic units of the Sierra Nevada are formally named after the iconic landmarks of Yosemite but currently lack formal stratotype designations. These units include: the Johnson Granite Porphyry; Cathedral Peak Granodiorite; Half Dome Granodiorite; Bridalveil Granodiorite; Leaning Tower Granite; Taft Granite; and El Capitan Granite. It is recommended that stratotype designations of these units be made in order to: A) provide a standard reference for scientific research; B) educate park staff and visitors about the geoheritage significance of these units; and C) help safeguard these exposures.

Figure 3. View from the top of Sentinel Dome, Yosemite National Park, showing weathering pans in the Sentinel Granodiorite. Inset image shows close-up textural detail of the granodiorite near the precipice of Yosemite Falls, penny for scale is 1.9 cm (0.75 in).

Photos courtesy of Allen Glazner (University of North Carolina) and Greg Stock (Yosemite National Park).

Additional Recommendations

The Geological Resources Division and park and network staff should work together to:

• Increase park staff awareness and understanding about the scientific, historic, and geologic heritage significance of geologic stratotypes.

• Ensure park staff are aware of the locations of stratotypes in park areas.

• Formally assess potential new stratotypes as to their significance, based on lithology, stratigraphy, fossils, or other notable features.

• Focus on registering new stratotypes at State, Local, and potentially Federal government levels where current legislation allows.

• Compile and update a central inventory of all designated stratotypes and potential future nominations.

• Regularly monitor geologic type sections to identify any threats or impacts to these geologic heritage features in parks.

• Obtain good photographs of each geologic type section within the parks, and potentially use photogrammetry to monitor geologic type sections.

• Utilize selected robust internationally and nationally significant type sections as formal teaching/education sites and for geotourism so that the importance of the national- and international-level assets are more widely (and publicly) known, using information boards and walkways.

• Develop conservation protocols of significant type sections, either by appropriate fencing, walkways, and information boards or other means (e.g., phone apps).

Definitions

Unit stratotype: the type section for a stratified deposit or the type area for a non-stratified body that serves as the standard for recognition and definition of a geologic unit (North American Commission on Stratigraphic Nomenclature 2005). Once a unit stratotype is assigned, it is never changed. The term “unit stratotype” is commonly referred to as “type section” and “type area” in this report.

Type locality: the specific geographic locality encompassing the unit stratotype of a formally recognized and defined unit. On a broader scale, a type area is the geographic territory encompassing the type locality. Before development of the stratotype concept, only type localities and type areas were designated for many geologic units that are now long- and well-established (North American Commission on Stratigraphic Nomenclature 2005).

References

Henderson, T., V. L. Santucci, T. Connors, and J. S. Tweet. 2021. National Park Service geologic type section inventory: Sierra Nevada Inventory & Monitoring Network. Natural Resource Report NPS/SIEN/NRR—2021/2219. National Park Service, Fort Collins, Colorado. https://doi.org/10.36967/nrr-2284063.

Bateman, P. C. 1961. Granitic formations in the east-central Sierra Nevada near Bishop, California. Geological Society of America Bulletin 72(10):1521–1537.

Bateman, P. C. 1988. Constitution and genesis of the central part of the Sierra Nevada Batholith, California. U.S. Geological Survey, Reston, Virginia. Open-File Report 88-382. Available at: https://pubs.er.usgs.gov/publication/ofr88382 (accessed December 7, 2020).

Bateman, P. C. 1992. Plutonism in the central part of the Sierra Nevada batholith, California. U.S. Geological Survey, Reston, Virginia. Professional Paper 1483. Available at: https://pubs.er.usgs.gov/publication/pp1483 (accessed December 7, 2020).

North American Commission on Stratigraphic Nomenclature. 2005. North American stratigraphic code. AAPG Bulletin 89(11):1547–1591.