|Three distinct layers of sedimentary material carried from high regions to the west were deposited over Southern Saskatchewan during the Cretaceous Period (60-130 million years ago). The first of these (the Bearpaw) often exceeds 1100 feet in thickness. It forms the subtract material to the north of the Missouri Coteau and is characterized by dark marine shale, bentonite layers, and sandstone tongues.
The second layer (the Eastend) shows a transition from marine to fresh water. It is characterized by rusty greenish to yellowish siltstones, sandstones, and mudstones. The upper layer is kaolinized. The third layer
(the white mud) is non-marine and varies from 0 to 45 feet in thickness. The white kaolinitic material with gray to black carbonaceous layers make it easy to recognize. It is exposed in the valley near Castle Butte,
Highway 34, and in the Cathedral area.
Two other layers (the Battle and the Frenchman) were deposited near the end of the Cretaceous period and while they were exposed in the Killdeer-Twelve Mile Lake area they appear to be absent in the Big Muddy.
During the Paleocene era, a layer (the Ravenscrag) up to 500 feet thick was deposited. It is characterized by coal beds, non-marine sands, shales, silts, and clays. Where exposed on a cliff face the lower edge is
gray and is called the "gray facies". The upper layer is brownish often containing white kaolinitic Willow Bunch member material. This layer is called the "buff facies".
In the Miocene a cabby gravel and crossbedded sand layer (the Wood Mountain) was deposited over the Ravenscrag.
The Ice Age (Pleistocene) changed the face of this area. To the north the ice sheets were much thicker but to the south they were non-existent. The Big Muddy is a melt water channel that carried vast quantities of
water eastward. Sediment was deposited forming deltas of fine silt and sand. Terminal moraine, ground moraines, and hummocky moraine form the major landscape characteristics around the valley. Flat outwash areas
(Bengough, Saskatchewan is built on one) form flat fertile land.
In the recent period, erosion has served to round the hills, cut channels, and in general deposit material in the valley. This results in an area of interest to the professional and the sightseer.
The Big Muddy Valley runs generally south-southwest from Willow Bunch, SK. to around Plentywood Montana. The valley was formed at the end of the last Ice Age when melt water from the retreating glaciers carved most of
the fantastic scenery you will see on the tour.
This river carried the melt water clear to the Gulf Of Mexico. In some places the valley is a mile wide and 500 feet deep so this was a mighty river indeed. Today water on the south side of the Missouri Couteau still goes to the Gulf of Mexico. Although now water here travels to the Missouri River then the Mississippi River.
The valley comes by its' name quite honestly. The soil in the area is fairly light and contains a lot of fine silty clay which becomes very slippery when wet
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