Smoky Hill Chalk Member

The Smoky Hill Chalk Member is a soft chalk formation spanning multiple states with layered deposits of marine origin. These beds contain bentonite, jarosite, pyrite, and chert mixed throughout the chalk, creating a complex geological structure.

During the Late Cretaceous period, roughly 80 million years ago, a vast sea covered this entire region. The chalk layers accumulated gradually as shells and skeletal material settled on the seafloor.

The formations attract paleontologists and fossil enthusiasts who conduct field research and document findings. Important specimen collections housed in museums worldwide have been built from discoveries made here.

Visitors can access the formations at Monument Rocks and Castle Rock to examine the chalk cliffs up close. These public sites offer clear views of the geological layers and allow visitors to walk among the rock formations.

One of the most remarkable fossils is a Xiphactinus skeleton that contains another fish, Gillicus arcuatus, within its body. This specimen offers a rare glimpse of predator-prey interaction preserved from millions of years ago.

Location: Colorado

Location: Kansas

Location: Nebraska

Location: South Dakota

Part of: Niobrara Formation

GPS coordinates: 38.80250,-100.94250

Latest update: December 10, 2025 16:23