This location dramatically shows geologic features with Harney Peak Granite, black shale, and a fold you can trace with you hands, all exposed by road construction.
The large granite intrusion dominates one side of the cut while black shale provides a stark contrast on the other. Between the two, at ground level, is a geologic fold. Truly an inspiring sight.
The Black Hills are characterized by geology shaped by both ancient formations and more recent glacial activity. The region features Precambrian (4 billion to 540 million year) rocks, including igneous and metamorphic rocks, alongside sedimentary deposits laid down during the Mesozoic(250 to 66 million years ago) and Tertiary(66 to 2.6 million years ago) periods.
Harney Peak granite is large grain with crystals large enough to be seen and other materials, such as muscovite, quartz, pegmatite, mica(the shiny flaky flat stuff), hornblend(the black hexagonal crystals) that solidified during the slow cooling process.
Black shale is the dark colored, slab like rock formed during the Cretaceous period, 75 to 69 million years ago.
The peak of a geologic fold is in the middle of the rock cut. Geologic folds are formed when rocks are compressed, like compressing a multi-layer cake. Of course, the geologists have fancy names for the peaks and troughs of a fold.
To claim the earthcache:
- PHOTOGRAPH REQUIRED with the feature in the background.
- On which end (north or south) is the granite and shale?
- Is the exposed part of the fold a syncline or anticline?
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