Agate Fossil Beds National Monument
Agate Fossil Beds National Monument
Natural “depository” of an extinct animal community on the Niobrara River, northwestern Nebraska, U.S. The beds, laid down as sedimentary deposits 20 million years ago, bear the remains of prehistoric mammals. Discovered c. 1878, the site was named for its proximity to rock formations containing agates. A national monument since 1965, it covers 2,269 acres (918 hectares).
This entry comes from Encyclopædia Britannica Concise.
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