Agate Fossil Beds National Monument is a U.S. National Monument near Harrison, Nebraska. The main features of the monument are a valley of the Niobrara River and the fossils found on Carnegie Hill and University Hill.

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Agate Fossil Beds National Monument
IUCN category III (natural monument or feature)
University and Carnegie Hills fossil beds
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Location	Sioux County, Nebraska, United States
Nearest city	Harrison, NE
Coordinates	42°25′18″N 103°45′14″W[1]
Area	3,057.87 acres (12.3748 km2)[2]
Established	June 14, 1997
Visitors	15,555 (in 2016)[3]
Governing body	National Park Service
Website	Agate Fossil Beds National Monument

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The area largely consists of grass-covered plains. Plants on the site include prairie sandreed, blue grama, little bluestem and needle and thread grass, and the wildflowers lupin, spiderwort, western wallflower and sunflowers.

Originally the Agate Springs Ranch, a working cattle ranch, was owned by Capt. James Cook. The monument's museum collection also contains more than 500 artifacts from the Cook Collection of Plains Indians artifacts.

The national monument was authorized on June 5, 1965, but was not established until June 14, 1997. The Harold J. Cook Homestead (Bone Cabin Complex) was listed on the National Register of Historic Places in 1977.^[4] Agate Fossil Beds is maintained by the National Park Service.^[5]

The site is best known for a large number of well-preserved Miocene fossils, many of which were found at dig sites on Carnegie and University Hills. Fossils from the Harrison Formation and Anderson Ranch Formation, which date to the Arikareean in the North American land mammal classification, about 20 to 16.3 million years ago, are among some of the best specimens of Miocene mammals.^[6]

Species found in Agate include:

• Miohippus, Merychippus and Parahippus, ancestors of the modern day horse.
• Diceratherium, two-horned rhinoceros.
• Menoceras, pony-sized rhinoceros, the most common animal found in the fossil beds.^[7]
• Daphoenodon and Ysengrinia, two types of mid-sized bear dogs.
• Promerycochoerus, a semiaquatic hippo-like oreodont.
• Daeodon, the largest Entelodont (giant pig-like ungulate).
• Stenomylus, gazelle-like camelids.
• Oxydactylus, giraffe-like camelids.
• Palaeocastor, land beavers that dug large corkscrew-shaped burrows (Daemonelix).^[8]
• Moropus, a chalicothere which are relatives of rhinos and horses.
• Merychyus, a sheep-like oreodont.
• Syndyoceras, antelope-like mammal and extinct relatives of artiodactyls.

• List of fossil sites
• List of national monuments of the United States
• Ashfall Fossil Beds
• Florissant Fossil Beds National Monument
• John Day Fossil Beds National Monument
• Scotts Bluff National Monument