The first chapter in the geological history of Oklahoma was the formation of granite and other rocks from molten material deep in the Earth's crust. These rocks are visible in the Arbuckle mountains and extend under the surface of the Ardmore Basin. This basement rock is the foundation on which all the younger rock rests. The oldest granite in the state is found in the Arbuckle Mountains near Tishomingo, and is 1.4 billion years old.

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