Cliffs, Caves & Crystals: The Pahasapa Formation

🚙 US-14A Mileage 2.1 GPS Coordinates N 44.27.364 W 103.51.757 3,917 ft.

Cliffs, Caves And Crystals Update2.pdf

Lesson Guide: PRINT

Field Exploration

No other geologic formation exemplifies the cliff-faced character of Spearfish Canyon more than the Pahasapa Limestone. In this exciting exploration you'll be introduced to its geologic story and be provided with an opportunity to peer into a roadside cave to examine some of the formation's amazing calcite crystals.

This pdf document contains the specific directions for reaching our featured Lesson Site as well as a detailed explanation of its geologic story. Mileage to the site as well as its specific coordinates are listed on the header above and also in the lesson document. Roadmaps and other learning aids can be found at the Lesson Resources link in the menu and are helpful to have handy in the field. Please print this document and take it with you or read it thoroughly before departing. 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.

Spearfish Stratigraphic Column

Note the position of the Pahasapa Formation. Age and thickness of geologic formations are approximate.

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

Pahasapa Formation

This view is looking west from the parking turnout at the Lesson Site. The Pahasapa Formation is a buff-colored limestone that was deposited in the ancient Mississippian Sea some 300+ million years ago. See the Stratigraphic Column on the left for the position of the Pahasapa Limestone within the formations exposed here in Spearfish Canyon.

Limestone Cave

This small cave is located directly alongside the parking turnout. Caves, like this one, often form in layers of limestone and are common features of the Pahasapa Formation.

Roadside Cavern

A cautious scramble up to the cave for a look inside reveals a significant number of calcite crystals. Calcite is a pure form of limestone in crystal form. Although the crystals resemble gemstones they are relatively soft and worthless. Many a miner, upon discovering calcite, has been fooled into thinking they've struck it rich. Keep your eyes open for other caves throughout Spearfish Canyon.

Calcite Crystals in Cavern

This photo was taken at arms length inside the small cave. The numerous calcite crystal that encrust the cave walls are a variety known as Dogtooth Spar.

Vertical cliffs of the Pahasapa Limestone

Vertical Cliffs of the Mississippian Pahasapa Limestone.

Most of the taller, vertical cliffs you'll see throughout the canyon are exposures of the Pahasapa Formation, a vast layer of limestone that formed from the accumulated remains of hard-shelled invertebrates on the seafloor.