A summary of existing knowledge of the correlation of the Jurassic rocks of considerable parts of Utah, Arizona, New Mexico, and Colorado was published by the writers in 1936.3 This summary was based on detailed mapping by several parties of the Geological Survey in southeastern Utah, supplemented by extensive reconnaissance examination by the writers in adjoining regions. The proposed correlations recognized the general equivalence of the Todilto limestone of northwestern New Mexico and northeastern Arizona with the “middle La Plata” of the San Juan Mountain region of southwestern Colorado, and the equivalence of the Entrada sandstone as defined and...

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