Geology of Little River Canyon National Preserve, Alabama

Part of the NPS Geodiversity Atlas, which describes each park's significant geologic features and processes. Geodiversity is the full variety of a park's natural geologic resources — rocks, minerals, sediments, fossils, landforms and physical processes — and its soils. The atlas comes from the NPS Geologic Resources Inventory.

The preserve's Geologic Resources Inventory report. Image from the NPS's page.

The preserve

Little River Canyon National Preserve, established on October 21, 1992, protects the natural, scenic, recreational and cultural resources of one of the most extensive canyon and gorge systems in the eastern United States, in northeastern Alabama. The Park Service manages 5,517.06 hectares (13,632.95 acres) with the Alabama state park system. The area is part of the Appalachian–Alleghanian mountain belt.

The rocks

The canyon exposes the lowest Pennsylvanian rocks, the Pottsville Formation:

• Lower Pottsville — massive, pebbly, quartz-rich sandstone, with shale, coal and mudstone, laid down in front of a delta and in barrier-island and back-barrier settings.
• Upper Pottsville — hard, crossbedded conglomerates and sandstones from a river-dominated delta, in repeating sequences of coal, shale and sand.

Beneath them, the canyon cuts into Mississippian carbonate rocks.

Little River Falls. Image from the NPS's page.

How the canyon formed

Little River Canyon is cut through the Lookout Mountain syncline, a broad, eroded downfold that dips gently to the southwest. The fold formed in the Alleghanian orogeny of the Pennsylvanian and Permian — the last great mountain-building event in the southern Appalachians, with continental collision, regional uplift, subduction, magma and extensive thrust faulting and folding. The Valley and Ridge rocks of Alabama rest on a huge décollement, a detachment surface along which the folded and faulted Paleozoic rocks were shoved westward; the Rome fault cuts Lookout Mountain to the south.

The landscape ranges from gently rolling uplands to sheer cliffs and the narrow canyon floor, with sandstone glades, steep rocky trails and many outcrops. The Little River and its tributaries — Wolf, Bear, Johnnies and Yellow Creeks — working on the rock beneath have made the scenery: the canyon itself, the 14-m (45-ft) Little River Falls and Graces High Falls, seen from overlooks along Canyon Rim Drive such as Canyon View, Lynn, Hawks Glide, Crow Point and Eberhart Point.

Geologic map of the preserve, from the Geologic Resources Inventory. NPS.

Maps and reports

The preserve's Geologic Resources Inventory products are in the NPS DataStore, and a Soil Resources Inventory project has been completed. The region's wider story is on the Appalachian Plateaus province page.

Little River Canyon. Image from the NPS's page.

Sources

Based on "NPS Geodiversity Atlas—Little River Canyon National Preserve, Alabama," National Park Service; a work of the United States government in the public domain. The atlas places the preserve in the Valley and Ridge province in one section and the Appalachian Plateaus province in another, and gives the syncline's relief as "305 m (1,040 ft)", figures that don't match; this page leaves both out.