... billion years ago. During the Mesoproterozoic era of the Precambrian eon, the continent spread apart on the Midcontinent Rift System extending from what is now eastern Lake Superior through Duluth to Kansas; this rifting process stopped before an ocean developed. A flow some 200 feet (60 meters) thick formed extremely hard volcanic rock which resisted a billion years of erosion which cut down surrounding formations.[2] This formed both Palisade Head and Shovel Point.” source: https://en.m.wikipedia.org/wiki/Palisade_Head
