One of the plants that loves degraded, rocky shale banks is the bird-foot violet, Viola pedata. At this site, however, we found some Viola pedata plants that made 2′ wide spreading patches, which I’ve never heard of or seen before. I’ve seen this species across the country and it always makes a small tight clump, so this is a huge variation from normal.
When I find Birdsfoot Violet in the forest it’s generally in small clumps or single plants.
Out in the full sun it grows in great drifts. Particularly along the roads in the Ozarks I’ve seen it as thick as the photo above but running for hundreds of yards.