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Geologic Map
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Generalized Geologic Map of the Conterminous United States
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  The North American Tapestry of Time and Terrain

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Crowleys Ridge


close up of crowley's ridgeCrowleys Ridge, evident on the map as a long yellow ribbon, is an erosional remnant of 40- to 50-million-year-old sedimentary rock in the upper Mississippi River Embayment. The ridge formed late in the Pleistocene as the river, gorged with glacial meltwater, continually shifted course and broadened its floodplain by eroding the Tertiary rock forming its banks. Crowleys Ridge is located near the site of the great 8+ magnitude New Madrid earthquakes of 1811-1812.