Artisan Earth: Differential Weathering
🚙 US-14A Mileage 0.9                  GPS Coordinates N 44.28.242  W 103.50.941    3,758 ft.
Artisan Earth Update2.pdfLesson Guide: PRINT
A delta forms along the shoreÂ
From sands entrained in flow
Then settle out in cross-bed formsÂ
Like artwork in a show
Field Exploration
Is it possible for an outcropping of rock be classified as a work of art? We think so, and in this exploration we'll introduce you to the ancient Minnelusa Sandstone, a formation whose unique appearance may just qualify it for a blue ribbon. At this lesson site you'll view one of the canyon's most stunning rock-faces and learn about the geologic processes that brought it to be!Â
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.
Minnelusa Outcrop along the east side of Highway 14A a short distance from the Spearfish Canyon Informational Kiosk and parking area. When driving up the canyon from the town of Spearfish, it's quite easy to miss the outcrop due its south-facing orientation. Please pay close attention to the traffic when looking for the outcrop and use caution along highway.
The roadside outcrop of the Minnelusa Formation is both spectacular and curious in its appearance. The depositional qualities of the Minnelusa sediments, along with their selective response to Weathering, has resulted in an exposure dominated by a myriad of eye-catching erosional textures. The Minnelusa is a shallow marine sediment laid down during Pennsylvanian and Permian Time some 300 to 250 million years ago. See the Stratigraphic Column below for the position of the Minnelusa Sandstone within the formations exposed here in Spearfish Canyon.
Alternating hard and soft layers create the beautiful ribbed texture. Magnified view from picture above.
Honeycomb Weathering is sometimes referred to as Tafoni. Magnified view from picture above.
Be sure to download our Onsite Geology Lesson PDF posted above for a detailed geologic investigation of this site.Â
Send comments to: partial.melting@gmail.com
The Minnelusa Formation contains some of the widest variety and most interesting sedimentary structures in the canyon. Â Age and thickness are approximates.