May 2020 • Nebraskaland 39
Rock into its unusual shape.
So, yes, the "Rock" is mostly clay. This
surprised some emigrants. "It is called
rock, but it is nothing but sand and dirt,"
wrote Alonson Sponsler in 1850. Sponsler
didn't know it, but it is also accurate –
and more awe-inspiring – to say that
Chimney Rock is made of bits of the Rocky
Mountains, and that it contains a good deal
of volcanic ash besides. Ancient volcanoes
in western Colorado erupted over millions
of years, mixing ash with the clay.
Particularly violent eruptions created two
lighter-colored bands of ash that are visible
in the rock's base and spire.
About fi ve million years ago, the North
Platte Valley started to erode faster than it
was built up. So why didn't Chimney Rock
erode away too? It might be the hard cap of
sandstone protecting the spire. Prominent
buttes such as Scotts Bluff are similarly
protected. Even so, wind and water
continue to wear the spire away.
Erosion isn't the only thing that aff ects
Chimney Rock's shape. Pieces have also
been broken off by lightning strikes. And
at least since the 1860s, rumors have
circulated that soldiers used to fi re cannons
at the Rock for target practice – but that
seems to be just a story.
An expanded visitor center with new
exhibits is scheduled to open later this year
at Chimney Rock National Historic Site. All
plans are tentative during these unusual
times, but be sure to stop at Chimney Rock
when you next visit western Nebraska
state parks.
N
Visit History Nebraska's website at
history.nebraska.gov.
Artist William
Quesenbury drew
Chimney Rock
in 1851, looking
southwest from
near present-day
Highway 92. History
Nebraska 8783-5
A bird's-eye view highlights the Rock's layers and sharp angles. How long
would it take to carve this using nothing but water and wind? History
Nebraska RG3319-PH1-44
Rock Last?
