You searched for: Place Windfall Hill Prairie Nature Preserve Windfall Prairie Seep, West facing bank of the Middle Fork of the Vermilion River. Danville NW 7.5 minute topo. Remove constraint Place: Windfall Hill Prairie Nature Preserve Windfall Prairie Seep, West facing bank of the Middle Fork of the Vermilion River. Danville NW 7.5 minute topo. Topic Poales Remove constraint Topic: Poales