In areas of Northeastern Minnesota, the bedrock is comprised of the 1,878 million year old Gunflint Iron Formation. The iron formation consists of black or gray chert alternating with black iron-rich layers. During the late Wisconsin glaciation, the southwest trending Rainy lobe left a large slab of iron formation laying vertical. The bedding planes of the surrounding iron formation is nearly horizontal, contrasting with the vertical bedding planes of this slab. The name given to this 25 foot slab is Magnetic Rock (though many areas of the iron formation are magnetic).
For a more picture heavy look at the hike into Magnetic Rock, click here. The trail is over a mile in length to the rock.
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