Quaternary, Tertiary and Late Cretaceous Igneous Rocks
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 Quaternary: Less than 2 million years ago
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 Pliocene-Miocene: 2 to 24 million years ago
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 Oligocene: 24 to 37 million years ago
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 Upper Tertiary: Less than 20 million years ago
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 Middle Tertiary: 20 to 40 million years ago
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 Laramide: 40 to 72 million years ago
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Sedimentary Rocks
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 Quaternary-Tertiary: Less than 4 million years ago
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 Upper Tertiary: 4 to 37 million years ago
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 Lower Tertiary: 37 to 72 million years ago
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 Upper Cretaceous: 72 to 95 million years ago
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 Upper Cretaceous: 95 to 115 million years ago
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 Lower Cretaceous: 115 to 144 million years ago
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 Jurassic: 144 to 208 million years ago
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 Triassic: 208 to 245 million years ago
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 Permian-Pennsylvanian: 245 to 320 million years ago
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 Mississippian, Devonian, Ordovician, Cambrian: 320 to 570 million years ago
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Cambrian & Precambrian Igneous and Metamorphic Rocks
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 Cambrian: 510 to 570 million years ago
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 Precambrian: 950 to 1,400 million years ago
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 Precambrian: 1,700 to 1,800 million years ago
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 Granitic: 1,000 to 1,400 million years ago
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 Granitic: 1,700+ million years ago
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