Ripple marks

Ripple marks in roadside outcrop south of Baraboo, WI. These ripple marks form as sand was deposited by a river about 1.5 billion years ago. Since then, the sand has turned into sandstone, been buried deep and metamorphosed into quartzite, unburied and eroded away as islands in an inland sea near the equator, buried again (shallower this time), and uncovered again.

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