Lycus Sulci is the region of hills and ridges located north and northwest of the famous giant volcano, Olympus Mons. The western margin of the Lycus Sulci meets the smoother Amazonis plains. This led some researchers to conclude that the two surfaces were in contact along a cliff. It was suggested that this might be the kind of cliff that forms from erosion by waves in a body of water as they break against a coastline.