Marker Logo HMdb.org THE HISTORICAL
MARKER DATABASE
“Bite-Size Bits of Local, National, and Global History”
“Bite-Size Bits of Local, National, and Global History”
Near Crawford in Sioux County, Nebraska — The American Midwest (Upper Plains)
 

Landscape in Layers

 
 
Landscape in Layers Marker image. Click for full size.
Photographed By Connor Olson, May 24, 2021
1. Landscape in Layers Marker
Inscription.  An immense geologic record of the earth's activity is exposed in this region of the Great Plains. Ninety million years ago, this area was a vast inland sea. Seventy five million years ago, the uplifts of the Rocky Mountains and Black Hills caused the sea to drain, transforming the ocean floor to a subtropical jungle - later becoming an Africa-like savannah - then the semi-arid grasslands you see today.

At Toadstool Geologic Park, the geologic record becomes visible at 34 million years ago. Then, heavy clouds of ash from Great Basin (Utah and Nevada) volcanoes blanketed the land. An ancient river carved the valley while the landscape changed to a semi-arid plain.

These layered rocks and clays reveal the area's natural history, exposed by the river that once flowed through here. Seasonal floods and volcanic ash reshaped the face of the land, adding new sediments to this floodplain, like new coats of paint. Eventually the layers were exposed as you see them today by the continuing wind and water erosion.

Toadstool:
not a toad nor a stool, but... a sandstone block resting on a small pedestal, resembling

Layers visible in the rock image. Click for full size.
Photographed By Connor Olson, May 24, 2021
2. Layers visible in the rock
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a mushroom, or a toadstool. This feature resulted from softer clay on the bottom eroding more readily than the more resistant sandstone blocks on top. Many have toppled over and many are still being formed.

Caption: Read the rocks and clays
Distinctive bands in the rocks and clay illustrate geologic processes that occurred millions of years ago. The bottom layers were deposited the earliest, and are the oldest. Colors are best seen in early morning or late afternoon when the sun is not directly overhead.

 
Erected by US Forest Service, Department of Agriculture.
 
Topics. This historical marker is listed in these topic lists: EnvironmentPaleontology.
 
Location. 42° 51.476′ N, 103° 35.047′ W. Marker is near Crawford, Nebraska, in Sioux County. Marker can be reached from Oglala National Grassland (Forest Road 902) 1.4 miles Toadstool Road. Located in Toadstool Geologic Park and Campground. Touch for map. Marker is in this post office area: Crawford NE 69339, United States of America. Touch for directions.
 
Other nearby markers. At least 8 other markers are within 15 miles of this marker, measured as the crow flies. Africa in Nebraska (here, next to this marker); Toadstool (here, next to this marker); Grassroots (here, next to this marker); The Innovation of Early Homesteaders (about 400

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feet away, measured in a direct line); Yellow Hand Monument (approx. 8.6 miles away); Battle of Warbonnet Creek Monument (approx. 8.8 miles away); Officers’ Row, 1909 (approx. 14.1 miles away); Buffalo Soldiers at Fort Robinson (approx. 14.2 miles away). Touch for a list and map of all markers in Crawford.
 
 
Credits. This page was last revised on June 11, 2021. It was originally submitted on June 8, 2021, by Connor Olson of Lemmon, South Dakota. This page has been viewed 66 times since then and 19 times this year. Photos:   1, 2. submitted on June 8, 2021, by Connor Olson of Lemmon, South Dakota. • Bill Pfingsten was the editor who published this page.

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Jun. 25, 2022