The ridges of the Keweenaw Peninsula are part of the Lake Superior syncline, which extends from northern Wisconsin to the tip of the Keweenaw Peninsula of Michigan. The Lake Superior shoreline also consists of rugged volcanic bedrock. Copper-rich lava flows, common on the Keweenaw Peninsula, were extensively mined. The Nonesuch shale also contains copper, but often in concentrations too low for profitable mining. The bedrock ridges of the Keweenaw Peninsula and of Isle Royale are both part of the Lake Superior syncline, which extends from northern Wisconsin to the tip of the Keweenaw Peninsula of Michigan.
Steep slopes occur along the north face of ridges, and high cliffs occur on the south face.
Narrow wetlands are found in many of the depressions between the parallel ridges of resistant conglomerate and amygdaloidal basalt. At the foot of ridges, the landscape is strewn with boulders. There are local areas of lacustrine sands, including small dunes, along the Lake Superior shoreline to the north. Broad areas of rocky ground moraine are in the west. Rocky, red sandy loams and silt loams.