Don't forget to stop and smell the primroses as you hike along the 1.5-mile Pawnee Buttes Trail, the only maintained hiking trail on the grassland -- and one where wildflowers bloom in the shadows of the 300-foot-high sandstone cliffs. In mid-June, when the prickly pear cactus, purple locoweed and white prairie phlox are blooming on the shortgrass steppe, the show is particularly brilliant, but spring's less showy displays are also rewarding. Donald L. Hazlett, a native of the eastern plains, has identified 521 different plants that grow on the grassland's 193,060 acres, including the Machaeranthera tanacetifoli (tansy aster), Ratibida columnifera (prairie coneflower) and Arenaria hookeri (tufted sandwort). His Vascular Plant Species of the Pawnee National Grassland is available at the U.S. Forest Service's office, which supervises the grassland, in Greeley.