Lakota gather with James Cook on the lawn at the Agate Springs Ranch in the early 1900s.

People have been part of the Agate Fossil Beds National Monument landscape for a long time, probably for at least 11,000 years. The valley landforms within the park have changed somewhat throughout time, as the climate changed and the river responded to variations in the amount of its flow and hence its channel configuration. The ecological interaction of people with the plants and animals, soils, bedrock, river, and climate make for a fascinating cultural story at Agate.

There is evidence of people's presence in the park about 2,500 years ago, when they camped along the Niobrara River--those ancient campsites are now evident on terraces 20'-25' above the modern river. People were probably hunting game in the valley (especially deer and buffalo but also rabbits, beaver, turtles, turkeys, and eagles), collecting everything from Indian turnip to wild plums to Indian grass, and replenishing their stock of stone tools. In the eighteenth and nineteenth centuries there is evidence that people from 31 of today's American Indian tribes used Agate valley resources--representing the Apache, Arapaho, Arikara, Cheyenne, Comanche, Crow, Dakota Sioux, Kiowa, Lakota Sioux, Nakota Sioux, Omaha, Pawnee, Ponca, and Shoshoni. Several sites and landscapes within the park are today considered to be sacred traditional Native American places.

In the late nineteenth century Euroamericans passed through (Lt. G. K. Warren) and then settled (The Grahams and Cooks) in the Niobrara Valley. The entire park is considered to be a cultural landscape, eligible for listing on the National Register of Historic Places. The interaction of the Cooks at the Agate Springs Ranch and Lakota Chief Red Cloud and his band is documented in artifacts and archives at Agate. Within the park, the Bone Cabin Complex is Register-listed because of its use as a homestead and paleontological research cabin. Park holdings include the Cook Collections, around 500 19th-20th-century Native American artifacts (e.g. beadwork, quillwork, catlinite pipes) and 10,000 archival records (papers and imagery) of the first 80 years of the Agate Springs Ranch. The North (Amherst), University, Carnegie, and Beardog Hills and Stenomylus and Daemonelix quarries are records of early twentieth century paleontological research that established new international records of Miocene mammals and their environment. Establishment of the park was authorized in 1965, to include 3,055 acres. In 2002, the established park included 2,270 acres of federally owned land, 293 acres as a private inholding (Agate Springs Ranch headquarters), and the remainder as scenic easements or state/county road rights-of-way.