Welcome to Medora, ND.
The crumbly, grey, popcorn-like rock that is found throughout the badlands is a type of clay called bentonite. It's not as glamorous as dinosaur fossils or as well known as coal but I think it's interesting just the same.
Bentonite is an absorbent aluminium phyllosilicate, impure clay consisting mostly of montmorillonite. The absorbent clay was given the name bentonite by Wilbur C. Knight in 1898, after the Cretaceous Benton Shale near Rock River, Wyoming.
There are different types of bentonite, each named after the respective dominant element, such as potassium (K), sodium (Na), calcium (Ca), and aluminium (Al).
Bentonite usually forms from weathering of volcanic ash, most often in the presence of water. However, the term bentonite, as well as a similar clay called tonstein, has been used to describe clay beds of uncertain origin
For industrial purposes, two main classes of bentonite exist: sodium and calcium bentonite.
When bentonite becomes wet, it soaks up water like a sponge and turns into a greasy mud that is very easy to slip on while hiking.
And now a bit about the badlands.
Areas of badlands topography are found in several places on the plains of the north-central US and the adjacent prairie provinces of Canada where erosion can be intense. The largest and best-known badlands in the United States are the extensive exposures of Oligocene-age beds along the White River in western South Dakota. In North Dakota, layers of sedimentary rock equivalent to those in South Dakota are found near Dickinson, where badlands are carved from the Oligocene Brule and Chadron Formations. In both states these beds are notable for their abundant mammal fossils. Other areas of badlands topography include exposures of the Eocene Golden Valley Formation, also near Dickinson, and exposures of the Cretaceous Hell Creek Formation.
During the Laramide, volcanoes erupting to the west spewed ash that was carried by the wind to western North Dakota where it washed into wet areas - lakes and lagoons. With the passage of time the ash was transformed to bluish, bentonite clay layers that can be seen today in the badlands areas.
The Sentinel Butte bentonite is an iron- and sodium-rich montmorillonite, one of three major Paleocene-age bentonites in North Dakota shown to have been derived from volcanic ash. The bentonites in the badlands can absorb up to several times their weight in water and they are extremely slick and mobile when wet. They form a characteristic popcorn-like surface when dry.
In order to be able to claim this earthcache as found you will need to send the answer to the following question to me by email.
Please do NOT POST your answer in your log.
1. What is the main mineral component of the bentonite found in this area ?
2. How large are the 'popcorns' pieces ?
3. In an area witgh a radius of approximately 5m (16ft) around GZ, tell me how many of these bentonite clay pieces do you see.
4. What colour are these bentonite pieces ?
5. As usual with earthcaches, a picture is optional but always appreciated.