Prairies and Grasslands

Sandy bank along the Arkansas River

NPS

Bent’s Old Fort National Historic Site features a reconstructed trading post located along the Arkansas River in the Lower Arkansas River Valley of southeastern Colorado. The river’s water supply and vegetation attracted American buffalo making this an ideal location for the Bent brothers to establish trade.

The park belongs to the western section of the Great Plains, stretching from the Rocky Mountains to the Missouri River. The shortgrass prairie which surrounds the fort receives an average twelve inches of rainfall each year. In this arid landscape, proximity to the adjacent Arkansas River was and continues to be crucial to life.

The broad flood plain cut a series of flat-topped hills, called benches, along the river’s flank. Because of the river’s course over time, elevation at Bent’s Old Fort gradually varies from 4035 feet to an average of 4300 feet north and south of the valley.

Plains cottonwoods and the peachleaf willow flourish along the Arkansas River, where water access is abundant. Historically, groves of trees like these served as building materials, fuel, and directional markers. The river bottom contains various mixed grasses, wetland, and riparian plant species. Riparian species, which thrive in floodplains, help to stabilize riverbanks during seasonal flooding.

Further out from the river, shortgrass prairie vegetation, mainly blue grama and buffalo grasses, once enticed large herds of grazing buffalo. Without these grasses, the buffalo robe trade at Bent's Fort would not have taken place. Typically, buffalo prefer the six inch tall short grasses to the waist-high varieties found within the extensive tall grass prairies to the east.

In addition to the common blue grama and buffalo grasses at Bent's Old Fort are other drought-tolerant species, such as sand dropseed grass, Western wheatgrass, and side-oats grama, which reach one to three feet in height. Dominant shrub species include sandbar willow and sand sage. Sandbar willow with its narrow, serrated leaves grows along rivers and areas prone to flooding, forming thickets three to twenty feet high. The sand sage plume with its aromatic, feathery, silvery-green leaves thrive in the sandy soil by the river’s edge. Both native and non-native species compete for survival in these alkaline soils. As a result, an ongoing park project is being conducted to remove non-native crop and exotic plants so that the native species flourish.

The landscape of the 1830s trading post, the native homelands of the southern Cheyenne and Arapaho, has changed in human use over time. It eventually drew in settlers with agricultural interests because of its abundant grazable grasslands. The prevlance of farming irrigation increased run-off and led to today's higher water table. At present, a marsh and wetland exist on fort grounds, where none existed two hundred years ago. Yet, traces of many original plant species are still seen growing as naturally as they did years ago within the wide-open spaces surrounding Bent’s Old Fort.

Text written by Volunteer Ellen Martin, 2025.

 

Buffalo grass grows plentifully on fort grounds.

NPS

Buffalo grass provides essential nutrients for grazing herds of buffalo - a must for the success of buffalo robe trading which occurred at Bent's Fort in the 1830s and 1840s.

 

Blue grama grasses are still seen across the landscape at Bent's Fort.

NPS

Blue grama is Colorado's official state grass. It and buffalo grass make up over 80 percent of the grasses that grow in the shortgrass prairie. Not only good nourishment for buffalo, birds and other pollinators benefit from its growth.