The scenery of the region between Split Rock and Beaver Bay resulted from important events of early geologic time. Lava flows that had accumulated there to a thickness of about 30,000 feet were lifted and arched by a huge mass of molten material rising through the earth's crust farther north. This mass, the Duluth Gabbro, is now extensively exposed in the Duluth area. The 100-foot-high lighthouse cliff is a fine-grained phase of gabbro named Beaver Bay diabase, whose massive resistant character makes the shore of this region particularly bold and rocky. At the base of the lighthouse on top of the cliff is another kind of rock, light green in color and coarse in texture, called anorthosite. This rock, anorthosite, shows an excellent exposure in the highway cut at Silver Bay and stands up as prominent rounded hills from Split Rock to Carlton Peak near Tofte.