North Dakota
White Butte |
Sedimentary |
|
|
|
|
Bedrock: Chadron Formation, White River Group |
Tertiary (Oligocene) |
|
The "dazzling white", gravel-bearing sandstone that caps White Butte has been informally called the Chalky Buttes member of the Chadron Formation. Thin conglomerate layers include clasts of chert, petrified wood, granite, rhyolite, and distinctive quartz-latite porphyry believed to have been eroded from the Beartooth Mountains. The sandstone is stained yellow by limonite toward the base, where it unconformably overlies the clay and silty claystone of the Amidon member. Geologists speculate that an ancestral Yellowstone River deposited these alluvial materials when it flowed south-southeast through Slope County, in a deep valley it had eroded into the older units below, much as the modern Missouri River is cutting into older rocks today north of Bismarck. The Chadron Formation has yielded titanotherium fossils near Rhame, southwest of the highpoint. (See Cenozoic titanotheres in the Jesse Hyde lantern slide collection, Case Western Reserve Geology department website.) Surficial Geology: Pleistocene glaciation did not reach quite this far south in the state. Erosion along tributaries of the Little Missouri River has formed the typical badland topography of western North Dakota: buttes capped by sandstone overlie more easily eroded clays. Soil Series: Badland/Cabbert complex: Shallow, light brown silt-loam soils over shallow bedrock, commonly gullied, suitable for carefully managed rangeland or wildlife habitat. Where the clay-rich Amidon member is exposed without vegetation and soil cover on the lower slopes of White Butte, the surface is covered by slippery clay which dries out to a "popcorn" texture (see photo below). |
||
Additional Photos: |
||
|
||
|
Selected References:
Other suggested sources of information:
|
||
