MANAGEMENT OF THE PURGATOIRE RIVER DINOSAUR TRACKSITE

In 1990, Congress passed Public Law 101-510, transferring a portion of the Purgatoire River valley of southeastern Colorado to the USDA Forest Service (FS). Known as Picket Wire Canyonlands, this deeply carved and rugged valley contains many significant historic and prehistoric resources. The primary purpose of the transfer directed the FS to protect and preserve an extensive assemblage of late Jurassic dinosaur trackways along the Purgatoire River. Often touted as the largest dinosaur trackway in North America, and bearing some of the first recognized evidence of herding behavior in dinosaurs in the form of parallel sauropod trackways, this site continues to receive scientific attention and thousands of visitors annually. Protecting the site is an ongoing challenge given the unpredictable flash flood nature of this river system. The management strategy combines research and recording with direct erosion control measures.

The dinosaur tracks are preserved in a durable but extensively jointed limestone bed, surrounded by friable mudstone. Current energy of the river was eroding the site, undercutting mudstone beneath the limestone and allowing mass wasting along the river’s edge. Over the last decade the FS has emplaced a series of erosion control structures to stabilize the edge of the limestone and bedrock within the river channel. Constructed from eroded blocks of the site itself and thus aesthetically transparent, the erosion control structures have built up protective sediment islands along the edge of the site which are now colonized by native riparian species, greatly reducing erosion of the site. Now that the site is stabilized, keeping the area free from burial by flood deposition of sediment and woody debris has become a periodic necessity.

Research and recording of the site continues by numerous methods, including direct molding and casting, recovery of eroded blocks, mapping and photography by aerial and ground based methods, and ground penetrating radar studies. Recent efforts to re-expose portions of the trackway buried by alluvium remind us the visible site is only a small portion of what must be a truly immense site in the subsurface.

Although erosive loss of trackways will doubtless occur in the long-term, there is equal certainty that large portions of the site will be maintained for future generations.