Somewhere around 500 million years ago, in the Paleozoic Age, there began the processes that created what is now called the Bighorn Basin.
Geologic evidence indicates that during the Cambrian Period, ancient seas advanced and retreated in the shale of the Gros Ventre Formation, and shale and Gallatin Limestone layers that form the bottom of the canyon. Above that lies the Bighorn layer of dolomite, formed during the Ordovician Period. The Jefferson and Three Forks, comprised of limestone, dolomite and shale, were the next layers formed, in the Devonian Period. Nearly 500 feet of Madison Limestone was added during the Mississippian and Pennsylvanian Periods. Unlike the barren bottom of the canyon, the Madison Limestone was formed of decaying prehistoric life whose remains are preserved in the rock. Capping all this is the Amsden Formation, formed about 250 million years ago during the Pennsylvanian Period.
Three major changes created the Bighorn Canyon during that time.
The ancient river, merely meandering then, ran over basically flat prairie land. The solid rock lay buried under sediments being carried in from the Rocky Mountains just being created.
Strong forces deep in the Earth’s crust forced the land to rise slowly. The river became trapped in its course which made it faster, and with this speed and scouring power it eroded the land and cut into the rocks as they rose higher.
The fast-running water washed away the old sediments. The upfolded rock became the Bighorn Mountains, and that is how the canyon with the river running directly through it – at times dropping 2,200 feet from the rim – came into being.
Yellowtail Dam on the Bighorn River is anchored on the canyon rim. The vari-colored rocks of the canyon are spectacular.
This dam was the key feature of the Pick-Sloan Missouri Basin Program, instituted to utilize the waters of the Missouri River Basin. The Yellowtail is the highest dam in the basin, rising 525 feet, and creates the Bighorn Lake reservoir.
It is also a major component in the Bighorn Canyon National Recreation Area, some 63,000 acres of paradise for outdoor lovers.
To get credit for the find, the following criteria must be met:
A picture is no longer required, but it would be nice to see you at that location!
1.) Email me the following information, which can be found in the Visitor Center:
a.) In what layer of canyon rock is the Yellowstone Dam anchored?
b.) What type of life was present during the Paleozoic Era and deposited in that rock layer?
c.) Which states are in the Pick-Sloan Missouri Basin Program Power System?
d.) Name the dams that are illustrated to demonstrate different engineering designs.
e.) The dam is named for Robert Yellowtail, a remarkable Crow Indian who lived to see 100 years. When was he chosen to represent the Crow Nation before Congress in Washington D.C.?
EarthCaches are educational by definition, that's why the questions. Answers ARE required.