Gravitation Greetings: The Kissing Rocks

🚙 US-14A Mileage9.3 GPS Coordinates N 44.23.577 W 103.54.715 4,796 ft.

Gravitational Greetings Update2.pdf

Lesson Guide: PRINT

Tumbling down from heights above

With seismic-level fun

The giant boulders came to rest

Within the Spearfish run

Field Exploration

Was that thunder I just heard or the sound of two giant boulders crashing into a riverbed? In this Spearfish Canyon exploration we take a look at the remnants of a rockfall event that took place in 1994. The sheer size of the boulders will amaze and the cause of the event will be investigated. Stay alert as you "Watch for Fallen Rock."

This pdf Lesson Guide contains the specific directions for reaching our featured site as well as a detailed explanation of its geologic story. Mileage and coordinates are provided in each document and roadmaps and other learning aids can be found at the Lesson Resources link in the sidebar menu. The document is most useful if taken with you to the lesson site. Exercise extreme caution at the lesson site and along roadways.

Are you ready. . . . Let's Go! S. V. Fogarty & W. R. Stevens

*Mileage starts at the intersection Colorado Bvd. and US 14A near Spearfish.

The Kissing Rocks

Limestone boulders from the 1994 rockfall event came to rest alongside the highway in the Spearfish Creek channel.

Overhead drone view of the "Kissing Rocks" lying beside the highway.

The Kissing Rocks Viewed From Above

Drone photo taken at an altitude of ~175 ft. AGL. Compare boulders to highway for scale.

Spearfish Creek flowing between the "Kissing Rocks."

The Kissing Rocks Underpass

Spearfish Creek flows between the two large boulders creating a natural eyelet.

Note the lighter colored rock exposure in the upper cliff of Pahasapa Limestone. This marks the original location of the boulders before becoming detached and falling to the valley floor. Examination of the landslide chute shorty after the event revealed that an unfortunate deer had been caught directly in the path of the tumbling boulders. Note the position of the Pahasapa Formation in the Stratigraphic Column to the right.

Note the position of the Pahasapa Limestone in the diagram above. Due to its high permeability and porosity, considerable amounts of water enter the Pahasapa Limestone and make it susceptible to weathering. Landslides such as this are common in the canyon but this one's proximity to the highway makes for an exceptional observational opportunity. Age and thickness are approximates.

Cliff Face Scar

Photo taken ~250ft. above the valley floor. Note the fresher-looking rock exposure near the lower center of the photo. This marks the attachment point of the boulders before falling. We personally don't know if one large mass fell and then fragmented upon impact or if each boulder broke off and fell independently. Fun to think about, though!

Be sure to download our Onsite Geology Lesson PDF posted above for a detailed geologic investigation of this site.

Send comments to: partial.melting@gmail.com

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