Near its southern end the parkway climbs onto a cap of Cretaceous gravel, rounded chert one to eight inches across set in a tripolitic sandy clay, as much as a hundred feet thick where the Collinwood quadrangle maps it. The ecoregion changes with the rock, from Interior Plateau to Southeastern Plains, inside a quarter mile of road in Wayne County, and some nineteen miles of parkway lie on the far side of that line. The highest ground on the whole Tennessee parkway, about 1,075 feet, sits on the gravel, the youngest formation the road runs on.
The deposit is easier to recognise by what it does than by what it is. Bedding is not discernible in it and its outcrops commonly have a bleached look. It thins northward, from a hundred feet to fifty, then thirty, until on the Gordonsburg and Henryville quadrangles it survives only in pockets too small to map.
The soils turn over with it. Brandon, Saffell and Lax take over from the Biffle and Bodine chert soils that carry the middle of the road, with about seven miles of parkway on Brandon alone. The gravel holds the crest for ten or eleven miles, then ends about eight miles short of Alabama. There the road comes back down onto Fort Payne chert and Chattanooga Shale, the Highland Rim's own rock, and stands on the Fort Payne at the state line, though the ecoregion map still calls it the Southeastern Plains.
Getting there
35.2326, -87.6995
Locations are approximate and may be inaccurate, on private land, or otherwise inaccessible. Check before you travel.
Hear it from the road
Whistlestop tells you this story automatically when you drive past. No searching, no tapping, nothing to ask.
