Crowley's Ridge is a geological anomaly within the Mississippi River alluvial plain. More than 150 miles long, it extends from southeastern Missouri deep into eastern Arkansas, spreading up to 10 miles wide and rising steeply as much as 250 feet above the surrounding plain. Geological evidence indicates the ridge was left standing between the ancestral Mississippi and Ohio rivers as they carved away the land to its sides. Wind-blown material, or loess, deposited over subsequent centuries added to the ridge's height, particularly along its southern reaches.
The Conservancy has designated the 22,600 acres of the St. Francis National Forest and surrounding lands as a priority conservation site. Most of the forest lies on the ridge near its southern end, but it also encompasses some 2,500 acres of bottomlands that include the only national forest shoreline on the Mississippi south of the river's headwaters in Minnesota.
The site's upland white oak-beech forest type has been described as more closely resembling that of Tennessee's distant hills to the east rather than that of the closer Ozark Mountains to the west. Highly susceptible to erosion, the ridge has been sculpted into a landscape that includes narrow gullies and steep slopes, creating microclimates that make for great diversity in plant species. Alligators are sometimes seen on ponds and oxbow lakes in the forest's bottomlands.
Wild habitats within the St. Francis site have been fragmented by changes in land use and affected by stream alterations in the vicinity that have disrupted natural water patterns.
Conservancy efforts with regard to the St. Francis National Forest site are in their initial stages. However, a donation of 97 acres adjacent to the national forest led to the creation in 2002 of the Conservancy's Burke Crowley's Ridge Preserve. Current and proposed Conservancy strategies include the creation of a science-based conservation plan for the site, acquisition of additional land to expand the national forest and working with the U.S. Army Corps of Engineers and other governmental entities to restore natural water regimes within the site.
Crowley's Ridge is a unique geological feature within the Mississippi River alluvial plain and the St. Francis National Forest's noteworthy assemblage of plant species, and it is unlikely these species would be present within the plain were it not for the ridge's topographical features and soil types.