In beautiful bluffs all over western North Dakota, a 65-million-year-old story of geology is told by the colors if you just know what you're looking at. And this Earthcache is geared towards showing you the stories of each layer and thinking critically of their formation by engaging with the cut in the Bluff at the posted coordinates. Questions can be found at the end of the geological information. Please practice leave no trace, respect the land around you, and pick up after yourself.
Layers:
Brick Red - Scoria or Clinker forms when coal veins catch fire and bake the rock above, changing it to a much harder, red rock.
Black - Lignite Coal veins are the remains of ancient plants and animals that lived in Everglades-type swamps.
Brown and Tan - sandstone, siltstone, and mudstone are sediments washed down from the Rocky Mountains.
Blue Grey - Bentonite Clay is made of ash from volcanoes.
Landscape:
In the Paleocene Epoch Era, modern day western North Dakota was a swampland. The west of North America was forming the Rocky Mountains, pouring large amounts of sediment east where they were deposited in this area in layers.⊃1; Volcanic eruptions over South Dakota, Montana, Idaho, Utah, and other western areas were spewing ash into the air and waterways, which carried a layer into the standing water of the swamps to create a layer of Bentonite Clay. Over time, these layers turned to a soft stone, which you can see exposed at this Earthcache.
The dry climate of western North Dakota keeps the landscape from eroding away quicker. The area averages 15 inches of rain each year, usually coming in errosive downpours of water that run down slopes and are sucked up into clay-rich rocks. This can cause hillsides to break and flow downhill.
Lignite coal veins can also form clinker (or "scoria") when encountered by prairie fires or lightning strikes. Coal veins can burn for many years and form a red natural brick layer above the vein, forming clinker. The dry climate, over time, will erode away the softer rock and leave behind ridges and buttes with durable red clinker caps.⊃1;
Questions:
Answer the following questions.
1. How many layers in the bluffs do you spot at Ground Zero? Identify them.
2. Feel the texture of the brown/tan color, what does it feel like?
3. Find a black layer in the bluff at or around ground zero, describe the texture of the layer.
4. Using the landscape surrounding Ground Zero and your knowledge of the area's geology, how do you think this cut in the bluff was exposed?
5. Post a photo with you, your caching party, or your GPS/a personal item on the trail to add with your submission.
Sources Cited:
"Geologic Formations" National Park Service - (https://www.nps.gov/thro/learn/nature/geologicformations.htm)