Smoky Hill Chalk Member, Paleontological formation in Western Kansas and Colorado, United States.
The Smoky Hill Chalk Member is a soft chalk formation found across parts of Colorado, Kansas, Nebraska, and South Dakota, made up of layers of marine shells and skeletal remains deposited on an ancient seafloor. The layers also contain bands of bentonite, jarosite, pyrite, and chert mixed in between the chalk.
Around 80 million years ago, a shallow inland sea called the Western Interior Seaway covered much of central North America, including this region. Over time, the remains of sea creatures sank to the bottom, slowly building up the chalk layers that are visible today.
The chalk outcrops draw fossil hunters and researchers who come looking for marine reptiles, fish, and birds from the age of dinosaurs. Finds from this area have ended up in museums across the United States and beyond.
Monument Rocks and Castle Rock in Kansas are the easiest places to see the chalk cliffs up close, and visitors can walk right among the formations. Both spots are on open land with little shade, so visiting early in the day makes the experience more comfortable.
A Xiphactinus fossil was found with a fully intact Gillicus arcuatus still inside its body, a rare case where both predator and prey are preserved together. The prey fish was large enough that swallowing it apparently killed the predator.
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