In its day, this garden was an engineering marvel. Avery Island is an extruded "bubble" of a salt dome, formed from the salt of an ancient Jurassic sea that left a vast bed of salt far below the marshy surface along the Louisiana coast. Over the millennia, the Mississippi River laid down layer after layer of sediment over this salt bed. The weight of the sediment caused the more buoyant salt to rise up through unconsolidated places in the overlaying sediment - much like toothpaste being squeezed from a tube - thus creating domes of salt below the Gulf Coast's soft subsurface.The Avery Island salt dome has actually broken through the surface of the earth, rising over 150 feet above sea level. The dome is estimated to be over 26,000 feet deep, nearly the size of Mount Everest.During frequent rains here along the Louisiana coast, water runs off the hills of Avery Island with enough volume and speed to erode the relatively thin layer of topsoil. Sunken Gardens represents McIlhenny's attempt to slow the rush of water during heavy rains, and create a quiet garden in the process. (Marker Number 14.)
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