Shape Shifters: Structural Folds

🚙  US-14A Mileage 6.3                                                  GPS Coordinates  N 44.24.971   W 103.53.248        4,349 ft.

Shape Shifters Update2.pdf

Lesson Guide: PRINT

Field Exploration

Don't look now but the roadside rocks just changed their shape! It appears that solid rock is not as solid as you thought, so in this exploration we'll introduce you to the science of structural geology alongside a magnificent roadside fold. What forces produced it and why is it here? We'll ponder these questions and more in our quest for understanding this amazing feature.

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.

Panorama of Tilted Cambrian Deadwood Formation

The dipping and contorted strata featured in this photo are of the Deadwood Formation. The fact that these sedimentary rock units are not lying in a horizontal position indicates that they were deformed sometime after their initial deposition in an ancient sea. Parking for this site is visible along the bottom edge of this photo. Please exercise extreme caution along the highway.

Structural elements of the monoclinal fold in the Deadwood Formation.

Structural Elements of the Monocline. 

To provide insight into how a structure may have formed Geologists like to describe the structure in terms of its geometry and directional orientation. These qualities are depicted in our annotated photo and can be measured with a compass and a level.

Monoclinal fold in the Deadwood Formation.

Road-level Close-up of the Plunging Monocline. 

The word monocline is derived from the words "mono" meaning one, and incline in reference to a layer's orientation with respect to a horizontal plane – a tilt or a bend. In our case the rock layers are interrupted by a single step-like fold or bend, thus mono-cline. We add the word "plunging" to denote that the entirety of the beds has a regional dip as well. 

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

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