fossil-rich mountain valley in central Colorado, U.S. It is located in the Rocky Mountains west of Pikes Peak and Colorado Springs. The monument preserves the fossil beds of the Florissant Formation, which consist of light gray shales dating from the Oligocene Epoch (33.7 to 23.8 million years ago). These deposits are particularly rich in fossil plants, including the petrified stumps of redwoods, and fossil insects. Created in 1969, the monument covers an area of 9 square miles (23 square km).

About 35 million years ago the area was a forested valley dominated by a large lake; volcanic eruptions buried the valley, petrified trees, and created layers of sediment in the lake bottom that preserved the plants and animals buried there. The site was discovered in 1873 and took the name of a nearby town (named by an early settler for his Missouri hometown; the French word for “flowering,” because of its abundant wildflowers). Tens of thousands of fossils have been collected at the site, and some are displayed at the visitor centre. The land is covered by forest (ponderosa pine, fir, spruce, and aspen) and meadow that support deer, pronghorn, elk, coyotes, black bears, mountain lions, and bird life. Area history is preserved in the Hornbek Homestead (1878).