Pompey's Pillar
Pompey's Pillar is an isolated remnant of more extensive Upper Cretaceous sandstone. It was cut out of the same rock that forms cliffs all along the river in this area. Because the sand grains are only loosely cemented together, the rock is relatively easy to carve. Fractures through the sandstone leave large flat faces as it erodes. This combination has made it a popular bulletin board for carvings and signatures from prehistoric to modern times. Clark's signature here is the only known remaining one from the Expedition.




The top of Pompey's Pillar provides a good vantage point for the area. Here the view is back up the Yellowstone River.