Mid-Week Geology Field Trip
Fluvial and Hypogene Speleogenesis in the McCloud Limestone, Shasta County, California
- By Joel Despain
- Departs from the registration tent at CoS
- Thursday, July 1, 2021 at 1:00 PM
- Sponsored in part by the National Cave and Karst Research Institute
Field Trip Overview
In an igneous land dominated by volcanoes and steaming hydrothermal vents, sedimentary and metamorphic rocks are the last thing you'd expect to discover. Yet, to the south and west of Weed, California, these ancient rocks persist. These are the remnants of coral islands from a Paleozoic ocean. In fact, they predate the geologically recent volcanic landscape by about 250 million years. Ages of tectonic shift slowly scraped those ancient islands off the seafloor and accreted them to the North American Plate. If you need a heavy dose of limestone geology during your convention week, here it is.
This is a geology field trip for agile cavers. While no technical skills are required, participants should expect an excessive amount of walking.
The Lake Shasta Caverns are a network of caves located on the McCloud arm of Shasta Lake in California. It was formerly named Chalk Cave and Baird Cave. The caverns are hypothesized to be between 750 and 450 thousand years of age. The caves are made entirely of limestone. Dave Bunnell photo.
Our field trip will depart and return to the College of Siskiyous campus - site of the NSS Convention. Unlike the Sunday trip, meals will NOT be provided so please plan ahead.
This trip will include extensive walking along roadways, paved cave tour trails and stairs and uneven trails on the surface. We will visit Lake Shasta Caverns, which includes hundreds of ascending and descending stairs. The informal trail to the entrance of Sa-wel Cave is uneven and includes a little bit of minor scrambling over rocks. In order to visit Lake Shasta Caverns during the busy summer season, the field trip will start mid-morning and will extend into early evening.
We will have four stops on the field trip. Stop 1 is at McCloud Reservoir to see two fluvial caves formed on Battle Creek a tributary to the McCloud. Stop 2 and 3 will be along Gillman Road along the upper McCloud River Arm of Shasta Reservoir. Here we will visit the entrance to hypogene Sa-wel Cave and will stop again to discuss another important cave in the area. Our final stop will be at Lake Shasta Caverns. To reach the cave we will travel by boat across the reservoir and up a private road two miles to reach the cave entrance, nearly 300 m above water level. We will tour the cave with Joel Despain and Pat Kambesis leading the walk-through.
The field trip will include a guidebook, and we plan to share and pass around maps, rock samples, copies of papers and other items of interest during the trip. We hope you will join us.
Geology and Research Background
The McCloud Limestone outcrops for 55 kilometers in a north-south orientation in the eastern Klamath Mountains between Redding and Mt. Shasta, California. The outcrop ranges in width from 100 m to 5 kilometers and is early Permian and highly fossiferous. It parallels the McCloud River, a popular trout stream that drains into Shasta Reservoir. The McCloud is a prominent unit that develops cliffs, massifs and small mountains 1000 m in height. Sa-Wel and Potter Creek caves were famous in the early 1900s for their contributions to Pleistocene paleontology and archaeology. Today the best known cave is commercialized Lake Shasta Caverns.
The Lake Shasta Caverns currently attract thousands of visitors every year. The only transportation to the caverns from the visitor center is a short ride on a catamaran across Shasta Lake, followed by a scenic bus ride up a steep mountain grade. The bus ride terminates at the cavern entrance. The site was declared a National Natural Landmark in May 2012. Dave Bunnell photo.
Some forty caves are reported in the McCloud Limestone. We studied an accessible subset of these to seek an understanding or the caves' geomorphic histories and origins. We made highly detailed maps of the caves to analyze their morphology (Kambesis, 2014) and used comparative morphology charts as developed by D'Angeli, et al. (2018). We analyzed the chemistry of local karst springs to assess on-going karst hydrology. We studied cave deposits including sediments, speleothems and secondary minerals, as well as primary porosity, morphology, structural control and other parameters influencing the development of cave voids. Diorite dikes found within the caves, the limestone and in surface outcrops were thin sectioned for mineralogical analysis to determine degree of alteration by apparent hot, chemically aggressive fluids. We have used work by other authors to temporally constrain the development of some caves in the study (Oester, pers. comm.).
The caves are highly varied but fall into two distinct groups. Some are horizontal and lie low on the landscape and contain or are near streams. These caves house copious sediments and indicators of fluvial development such as scallop and vadose canyons. Another set of caves lies high on the landscape, up to 400m above base level. Passage development in these caves is dominantly vertical with numerous pits and narrow rift passages but also a few very large rooms. These caves contain almost no sediment of any type and are dry except for speleothem drips. Diorite dikes in these caves are highly altered and are pyritized, sassuritized and serpentinized with more results still forthcoming.
We contend that one set of caves in the McCloud developed through frequently encountered karst geomorphic processes include carbonic acid chemistry, stream piracy, sediment flux and structural control. These caves are comparatively young, are still in primary development, and contain few speleothems. The second set of caves developed due to hypogene and volcanogenic speleogenesis between 750 and 450 thousand years ago under a regime of sulphuric acid chemistry. These caves include large masses of speleothems developed over time in these old caves.
Field Trip Details
Pat Kambesis, PhD
Center for Human GeoEnvironmental Studies, Western Kentucky University
Joel Despain, MS
National Cave and Karst Research Institute (Ret)
This event has a group limit of 25 participants maximum. Once that limit is reached, a wait-list will be established.
Age limits are 18 and above (or 14 and above with adult accompanier).
Field Trip Contact:
Joel Despain, MS NCKRI
To register for this event, please select "Mid-Week Geology Trip" on your convention registration form. There is an additional fee for this event.
Participants MUST be aware that this trip includes extensive hiking, stair climbing and cave exploring. While our mobility-impaired cavers are welcome to attend, not all facilities meet ADA requirements.
This trip will likely return to campus after the salon awards. Our scheduling options for this trip were limited and we had few options other than Thursday. If you attend this field-trip, you will likely miss the photo salon awards.
Today's Weather: Mount Shasta, CA
- Updated: Wednesday, February 24 at 7:39 pm
- Reporting Station: Mount Shasta (KMHS)
- Elevation: 3,540 ft.
- GPS: 41.31494;-122.31702
- Data provided by: National Weather Service
Barometer: 30.38 in.
Visibility: 10.0 miles
Tonight: Mostly clear. Low around 26, with temperatures rising to around 28 overnight. South wind 1 to 7 mph.
Thursday: Sunny. High near 53, with temperatures falling to around 50 in the afternoon. Northeast wind 2 to 10 mph.