Driving north on US 85 from Colorado through Cheyenne, Torrington, Lingle, Lusk and Newcastle, Wyoming.

We are heading to Custer State Park in South Dakota and driving north on US 85 through eastern Wyoming.

Volcanic ash seen from US-85 in eastern Wyoming

These cliffs look so much like chalk to me, but it isn't. I checked my Roadside Geology of Wyoming book and it appears that these white formations are white claystone and sandstone of the Arikaree formation.

The white color in these claystones comes from volcanic ash deposited here around 25-million years ago.

Ancient volcanic ash in eastern Wyoming

This is some more of that pale, soft sandstone and white claystone full of volcanic ash deposited here 20 to 25-million years ago.

Eastern Wyoming landscape with volcanic ash visible on horizon

Cattle are in the distance with several horses in the foreground. Eastern Wyoming is an area of vast prairies. The white cliffs in the background are volcanic ash.

Eastern Wyoming open prairie and volcanic ash deposits

The wide open space in this area fascinates me. There are enough cattle on this range to keep the grass cropped short yet we do not see any in this picture.

In the distance you can see cliffs of volcanic ash.

More of that ancient volcanic ash in eastern Wyoming

This is more of that eastern Wyoming volcanic ash.

Eastern Wyoming volcanic ash now classified as soft claystone and sandstone

These white outcroppings of soft claystone and sandstones fascinate me. Geologists believe that the volcanic ash was blown here on prevailing westerly winds from eruptions in Nevada where large volcanic eruptions of rhyolite ash occurred during the same time period this layer of sediment was deposited.

That is all there is for the volcanic ash of eastern Wyoming along US-85.

That is all there is.

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