Lavender Limestone: The Englewood Formation
๐ US-14A Mileage 4.1 GPS Coordinates N 44.26.253 W 103.52.379 4,048 ft.
Lavender Limestone Update2.pdfLesson Guide: PRINT
The purple rock of which its formed
Is layered, tough and bold
And holds within it evidence
Of oceans deep and old
Field Exploration
Something unusual was occurring in the sea 360 million years ago as evidenced in our featured rock formation. In this self-guided exploration you'll be examining the transitional boundary between two great geologic formations and contemplating the subtle yet significant changes that were taking place in the ancient ocean. We promise you won't be disappointed!
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 formational contact between the Lavender Englewood Formation and lighter Pahasapa Formation as seen at the lesson site just south of the parking area. See the Stratigraphic Column on the right for the position of the Englewood and Pahasapa Formations within the stack of rock layers exposed here in Spearfish Canyon.
Englewood Pahasapa
Sitting just at the base of the Pahasapa, the Englewood Formation is one of the thinner rock units in the canyon. Age and thickness are approximates.
Engelwood / Pahasapa Contact
These two formations formed in a shallow sea. The lower Englewood Formation formed during the transition from Devonian to Mississippian Time while the upper Pahasapa Limestone formed entirely within the Mississippian.
This picture displays a more defined contact not far from the study location. We did not include it in our lesson of study because of its unsafe proximity to the highway.
Formation Contact
The Englewood / Pahasapa contact is sometimes obvious in the surrounding cliffs due to the contrast in formational colors. The Englewood is the lower, brightly-colored formation.
Be sure to download our Onsite Geology Lesson PDF posted above for a detailed geologic investigation of this site.
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