The Louisiana Purchase State Park preserves ancient geological history and more recent American history. Once the Mississippi abandoned the Western Lowlands, headwater swamps formed in shallow basins surrounded by high terraces of glacial outwash. Groundwater rising to the surface and rainwater washing off the terraces flow into a clay bowl lined with thick muck. Such swamps do not experience the extremes of water levels that riparian systems do.
At the Louisiana Purchase swamp levels vary from the shallow perimeter of the wetland to the center. In a drought or even in late summer the swamp may dry out. Over time cycles of flooding and drying, though never extreme, have produced a complex vegetative community. Tupelo, bald cypress, black willow dominate the center of the swamp, where water during the growing season can be one meter deep. Buttonbush is one of the few species that occupies the understory. During the growing season herbaceous plants take root on the stumps of dead trees or in moss that grows on tree trunks right above the stable water level. Mixed in are lowland hardwoods–green ash, overcup oak, and Nuttall oak, which dominate the perimeter forest.
A boardwalk allows the visitor to walk from the perimeter forest to the center of the swamp.
In 1977 the state of Arkansas purchased a thirty-seven acre tract in the swamp to commemorate the Louisiana Purchase. When the United States acquired the Louisiana Purchase from Spain in 1803, it needed a point from which to conduct its survey of the new territory. Surveyors located their point in this headwater swamp in Arkansas.
On October 27, 1815 Prospect K. Robbins led a survey team from the confluence of the Mississippi and Arkansas Rivers. Traveling north from its starting point, the team established the north-south line known as the Fifth Principal Meridian. On the same day Joseph C. Brown led a similar team west from their starting point at the confluence of the Mississippi with the St. Francis. Robbins’ and his team traveled fifty-six miles north before they crossed the baseline laid down by Brown’s team at a point twenty-six miles from their starting point. The surveyors marked two eighteen inch tupelo trees as witness trees as the initial point from which the whole of the Louisiana Purchase would be surveyed. Beginning in 1820 the United States laid out its public lands in a system of townships. Surveyors split each square township into thirty-six mile-square sections. The Louisiana Purchase Historical Monument in the park preserves this point from which the survey started.[i]
[i] Taylor, Jim, “Swamp Makes History Personal at Louisiana Purchase State Park,” Arkansas Travel.com, http://www.arkansastravel.com/archives/printable_popup_botframe.sap?id=145; Arkansas Multi-Agency Wetland Planning Team, “Wetlands in Arkansas, Headwater Swamp,”http://www.mawpt.org/wetlands/classification/community_types.asp?showDetail=1&communityType=Headwater+Swamp; Arkansas Natural Heritage Commission, System of Natural Areas, “Louisiana Purchase Natural Area,” http://www.naturalheritage.com/system/detail.asp?map_num=46; Klimas, Charles V., Murray, Elizabeth, O., Pagan, Jody, Langston, Henry, and Foti, Thomas, A Regional Guidebook for Applying the Hydrogeomorphic Approach to Assessing Wetland Functions of Forested Wetlands in the Delta Region of Arkansas, Lower Mississippi River Alluvial Valley, Ecosystem Management and Restoration Research Program, U.S. Army Engineer Research and Development Center Environmental Laboratory, Vicksburg: September 2004, 50, http://el.erdc.usace.army.mil/wetlands/pdfs/trel04-16.pdf.