LaRue-Pine Hills is one of the most unique areas in the world. As with many places in the Shawnee National Forest, the beauty we see today is rooted in geologic history. Here at LaRue-Pine Hills it took millions of years to form its bedrock before nature’s erosive forces took over and created the 150-foot limestone bluffs that now rise out of the Mississippi floodplain. These massive bluffs extending roughly 5 miles along Highway 3 are as impressive today as they were to explorers Lewis and Clark in 1803. While traveling up the Mississippi River, Captain Meriwether Lewis writes in his journal: Novr. 22ed 1803 …but here putts in some high clifts the summits of which are crowned with pitch-pine & seeder,these rocks are nearly perpendicular in many places sixty feet , and the height of the hills appear about to be about 120 feet above the banks which forms their base…
LaRue-Pine Hills’ unique physical characteristics dictate and support a rich biodiversity not found anywhere else in the country. In all, the area covers about 4.5 square miles (3547 acres) and contains 14 natural communities including forests, wetland, prairie, glade and barren ecosystems and geologic features. Please help protect this special place for future generations to enjoy, study and appreciate.
At a Glance
The Research Natural Area
LaRue-Pine Hills/Otter Pond became our nation’s 250th Research Natural Area (RNA) in 1991. RNA’s are permanently protected to maintain biological diversity and to provide places for research and monitoring of undisturbed natural areas. This 2,811-acre tract includes LaRue Swamp, the Pine Hills (named for the stands of native shortleaf pines on the bluffs) and Otter Pond. Collecting of any kind is prohibited.
The geologic story of LaRue-Pine Hills begins millions of years ago when most of Illinois was a large inland sea known as the Illinois Basin. Over time the sandy shores of this sea became the sandstone rock formations one sees throughout southern Illinois. The deepest portion of the sea became the towering limestone bluffs at LaRue-Pine Hills. The rocks that make up the bluffs at LaRue-Pine Hills are Devonian age Bailey Limestone (about 408 million years old). Limestone is composed of lime (precipitated calcium carbonate) from the shells of dead sea animals (i.e., sea shells, coral, etc.). Over millions of years these layers of shell deposits were pressed into rock. Once the sea receded, this bedrock was exposed to nature’s erosive forces. Wind and water began to wear away the rock creating ridges and gullies, carving out the beautiful limestone rock formations of LaRue-Pine Hills.