Florissant Fossil Beds National Monument
Location: Teller County, Colorado
Time: 35 to 33 million years ago, during the Tertiary period
About this Famous Find: Florissant Fossil Beds National Monument is located in the eastern Rocky Mountains, west of Pikes Peak in south central Colorado. Noting the valley’s lush green forests and meadows filled with wildflowers, a settler in the 1800s gave this area the name Florissant, which means flowering in French. Around 4030 million years ago, though, this area looked quite different. Nearby volcanoes towered over valleys filled with forests and meadows and Great Lake Florissant stretched for nearly 15 miles.
The formation of the valley we see today at Florissant can be divided into several episodes. Uplift of the area and other parts of the Rockies and the Colorado Plateau began in the Late Cretaceous (~ 72 million years ago). During the Eocene (~ 34 million years ago), episodes of volcanism and erosion left behind the ash layers, basalt flows, and volcanic breccias that are now interbedded with the lake deposits. Together, these volcanic and lake sediments form the Florissant Formation. Through the Miocene and Pliocene (~ 24 to 3 million years ago), uplift and the resultant faulting blocked off the drainage of Lake Florissant and the lake began to fill up with sediment. Finally during the Late Pliocene (~ 3 million years ago), accelerated uplift brought Florissant Fossil Beds National to its present elevation of 8,400 feet.
The fossils from Florissant are well preserved within the fine-grained lake and ash deposits and include a wide variety of animals and plants. Fish, birds, opossums, horses, oreodonts, molluscs, and more than 100 species of plants and 1,100 species of insects have been described from these beds. The fossil insects and plants have been particularly valuable to paleontologists because these fossils are so delicate that preservation of this quality is extremely rare. In addition, the massive petrified tree trunks, buried and turned to rock after burial by the volcanic mudflows, provide a glimpse of what these ancient forests looked like over 30 million years ago.