Near Crawford in Sioux County, Nebraska — The American Midwest (Upper Plains)
Landscape in Layers
Photographed By Connor Olson, May 24, 2021
1. Landscape in Layers Marker
Inscription.
Landscape in Layers. . 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 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.
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 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
Click or scan to see this page online
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.
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.
Credits. This page was last revised on June 11, 2021. It was originally submitted on June 8, 2021, by Connor Olson of Kewaskum, Wisconsin. This page has been viewed 135 times since then and 8 times this year. Photos:1, 2. submitted on June 8, 2021, by Connor Olson of Kewaskum, Wisconsin. • Bill Pfingsten was the editor who published this page.
