The presidential proclamation which established Scotts Bluff National Monument in 1919 also established the Monument’s original boundaries.  This preserved some of the best native prairie in the region, prairie relatively untouched by human disturbance.

Natural prairie grasses are the predominant vegetation cover of the Monument's more level areas. Approximately 40% of the 3,003 acre Monument is mixed-grass prairie.  The prairie is dominated by blackroot sedge, and needleandthread grass, both cool season species. Together these two species are the dominant ground cover (82%). Other common native grasses of the prairie include western wheatgrass, junegrass, blue grama, prairie sandreed, and side-oats grama. Prairie vegetation is not only grasses. Forbs and shrubs also comprise the prairie vegetation. The most common forbs of the Monument include golden pea, scarlet globemallow (copper mallow), prairie coneflower, and dotted blazing star (dotted gayfeather). The most common shrubs include prairie rose, winterfat, western snowberry and fragrant sumac.