Welcome to Plentywood, Montana!
Plentywood is located in the Northeast corner of the state and has served as a trading post for the people living in that part of the state. Plentywood is a historical site as it is the site in which Sitting Bull and his Sioux people surrendered to the U. S. Army after living in Canada for five years. The Outlaw Trail crossed into Canada north of Plentywood. Rustlers moved their stolen cattle and horses along this passage across the border. Butch Cassidy named the trail and established a rest station in the Big Muddy Valley, west of Plentywood. At the turn of the century, the gulches around Plentywood harboured every manner of outlaw. This area was 'the Old West' legend.
Glacation:
Not only is this site historically important, but it is also a great site to showcase the geology of Montana. At this one site, you will learn how a slow moving chunk of ice sculpted the landscape you see before you. Actually it wasn't just a small chunk of ice. Far from it in-fact! The Laurentide Ice Sheet was a massive sheet of ice that covered millions of square miles, including most of Canada and a large portion of the northern United States, multiple times during Quaternary glacialepochs. It last covered most of northern North America between c. 95,000 and c. 20,000 years before the present day. At times, its southern margin included the modern sites of New York City and Chicago, and then followed quite precisely the present course of the Missouri River up to the northern slopes of the Cypress Hills, beyond which it merged with the Cordilleran Ice Sheet.
It is at this point that the the geology of the area gets interesting as it directly relates to the Glacial Erratic at ground zero! When the two ice sheets met, in what is present day Alberta, large boulders were transfered from the Cordilleran Ice Sheet to the Laurentide Ice Sheet. In what is called the Foothills Erratics Train, there is a stretch of 644 kilometres that contain thousands of boulders ranging in size from pebbles to immense boulders the size of a house. As the glaciers melted and retreated, they deposited the massive rocks into their present day locations. From the colour of the Erratic at ground Zero, we can tell that the likely source has been identified as being near Mount Edith Cavell in Jasper National Park. I'd tell you the colour and mineral of the glacier, but you'll have to visit the site to see it!
The other half of the equation, when it comes to the Badlands of Montana, is that after the great Glaciers retreated to form the land, it was erosion that striped back the layers of time to revel the millions of years of the earths history. Stream erosion, as well as wind and rain, carved the plains to reveal that they were deposited in layers. The layers are composed of tiny grains of sediments such as sand, silt, and clay that have been cemented together into sedimentary rocks. The sedimentary rock layers were deposited during the late Cretaceous Period (67 to 75 million years ago) throughout the Late Eocene (34 to 37 million years ago) and Oligocene Epochs (26 to 34 million years ago). Different environments—sea, tropical land, and open woodland with meandering rivers—caused different sediments to accumulate here at different times. The layers similar in character are grouped into units called formations. The oldest formations are at the bottom and the youngest are at the top, illustrating the principle of superposition.
Badland Formations:
Sharps Formation
The lighter-colored layer, that form the peaks and Badland canyons, was deposited from 28 to 30 million years ago by wind and water as the climate continued to dry and cool. Volcanic eruptions to the west continued to supply ash during this time.
Rockyford Ash
The thick layer of volcanic ash was deposited 30 million years ago, forming the bottom layer of the Sharps Formation. The Rockyford Ash is a distinctive marker bed used in geologic mapping.
Brule Formation
This tannish brown layer was deposited between 30 and 34 million years ago. As the climate began to dry and cool, the forest gave way to open savannah. Bands of sandstone interspersed among the layers were deposited in channels and mark the course of ancient rivers that flowed from the Black Hills. Red layers found within the Brule Formation are fossil soils called paleosols.
Chadron Formation
This greyish layer was deposited between 34 and 37 million years ago by rivers across a flood plain. Each time the rivers flooded, they deposited a new layer on the plain. Alligator fossils indicate that a lush, subtropical forest covered the land. Most fossils found in this formation are from early mammals like the three-toed horse and the large titanothere.
Yellow Mounds
The sea drained away with the uplift of the Black Hills and Rocky Mountains, exposing the black ocean mud to air. Upper layers were weathered into a yellow soil, called Yellow Mounds. The mounds are an example of a fossil soil, or paleosol.
Pierre Shale
The black Pierre Shale was deposited between 69 and 75 million years ago when a shallow, inland sea stretched across what is now the Great Plains. Sediment filtered through the seawater, forming a black mud on the sea floor that has since hardened into shale. Fossil clams, ammonites, and sea reptiles confirm the sea environment.
To register this find, you need to answers the following questions. I always try to respond to your emails ASAP, but if I don't respond it is safe to assume your answers are correct. I've also noticed recently that “teams” are having one member send in the answers for the rest of the team. This is fine by me but please note the names in the answer email so I can cross reference the logs with the answers. As always please do not post your answers with your log . . . please email them to me directly:
1. What colour is the nearby Glacier Erratic and what mineral is the erratic composed of based on the colouration?
2. Look to the hills beyond the Highway #5 and list the colours of the layers that you see? What formation do they belong to according to the above list?
3. What is the age of the oldest layer?
4. As an optional task, please take a picture of yourself at ground zero. Posing in front of the old tree stump is a good location! Please do not include the glacial erratic or the badland hills in the picture as it will give away the answers to the above questions.
Please note that this is an Earthcache, which means there is not a physical cache at ground zero. For more information on Earth caches, please visit www.geocaching.com or www.earthcache.org.
Sources:
http://www.nps.gov/badl/naturescience/geologicformations.htm
http://en.wikipedia.org/wiki/Glacial_erratic