Stop 6 - Hamblin-Cleopetra Volcano
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Volcanic rocks spread between Callville Bay and Echo Bay, along the shore of Lake Mead, are remnants of a giant volcanic mountain. The dark rocks in the background are all that remain of the eroded peak. Red sandstones of the Jurassic Aztec Fm. appear in the foreground. |
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Here the groups examines the well-preserved cross-bedding in the Aztec Fm. This cross-bedding is formed by wind deposition of sand, as on a desert surface. This desert existed about 170 million years ago and covered a large region of the US southwest. The Aztec Fm. correlates with the Navaho Fm. at both Arches National Park and Zion NP in southern Utah. Some have argued that these sands were deposited underwater, but that would not explain the presence of bird tracks on some of the bedding planes (found at other outcroppings of Jurassic sandstones). |
