Explore this remote preserve at Michigan’s northernmost tip where the horizon never ends. Note from Senior Scientist Dr. Doug Pearsall: Copper Harbor Conglomerate rocks at Horseshoe Harbor are sedimentary. A conglomerate rock is one that is formed by the deposition of sediments carried by streams. The Copper Harbor Conglomerate is formed by deposition of sediments that originated as rocks formed by subsurface flows of magma – so they are similar to volcanic rocks formed at the surface after an eruption. This magma flowed through fissures and cooled into igneous rock that was then eroded by streams, re-deposited, and cemented by ash and other fine sediments. These rocks are around one billion years old, which is really cool, and are the southern edge of a basin that dips under Lake Superior and re-emerges at Isle Royale and in northern Minnesota (also cool, at least to me).