Pictured Rocks National Lakeshore is a long, wonderfully scenic stretch of rocky cliffs along the southern shore of Lake Superior near the town of Munising (see map). The outcrops expose a succession of Proterozoic, Cambrian, and Lower Ordovician sedimentary rocks. The rocks are most easily examined from atop the cliffs and by boat.
The most distinctive overlook at Pictured Rocks is Miner's Castle. The rocks here are horizontally-bedded quartzose sandstones deposited in an ancient near-shore marine to beach environment. This is the type locality of the Miner's Castle Member of the upper Munising Formation (upper Middle Cambrian; often misinterpreted as Upper Cambrian).
Above & below: Miner's Castle, with quartzose sandstones of the Miner's Castle Member, upper Munising Formation, upper Middle Cambrian.
The oldest rock unit exposed at the surface in the Pictured Rocks area is the Jacobsville Sandstone. Only the uppermost portions of the Jacobsville outcrop above lake level in this area. The most easily examined Jacobsville outcrops here are at Miner's Beach, at the mouth of the Miner's River.
The cliffs at Pictured Rocks are almost entirely composed of shallow-water marine sandstones of the Munising Formation (upper Middle Cambrian). The lower contact with the Jacobsville Sandstone is a significant unconformity. The Munising at Pictured Rocks consists of a lower Chapel Rock Member and an upper Miner's Castle Member. The cliffs have extensive multicolored stains, the result of seeping groundwater and surficial water cascading down cliff faces. The colors are a principally a mix of stains from weathering and the presence of organics. The cliffs vary in morphology from irregularly vertical rock faces to steeply sloping and undercut cliffs. In places, erosive wave action has produced arches.
The Chapel Rock Member has a well developed basal conglomerate unit with cross-bedded quartz-pebble conglomerates and pebbly sandstones (see the 2 photos below).