Geologic Map of the Central Marysvale Volcanic Field, Southwestern Utah

The geologic map of the central Marysvale volcanic field, southwestern Utah, shows the geology at 1:100,000 scale of the heart of one of the largest Cenozoic volcanic fields in the Western United States. The map shows the area of 38 degrees 15' to 38 degrees 42'30' N., and 112 degrees to 112 degrees 37'30' W. The Marysvale field occurs mostly in the High Plateaus, a subprovince of the Colorado Plateau and structurally a transition zone between the complexly deformed Great Basin to the west and the stable, little-deformed main part of the Colorado Plateau to the east. The western part of the field is in the Great Basin proper. The volcanic rocks and their source intrusions in the volcanic field range in age from about 31 Ma (Oligocene) to about 0.5 Ma (Pleistocene). These rocks overlie sedimentary rocks exposed in the mapped area that range in age from Ordovician to early Cenozoic. The area has been deformed by thrust faults and folds formed during the late Mesozoic to early Cenozoic Sevier deformational event, and later by mostly normal faults and folds of the Miocene to Quaternary basin-range episode. The map revises and updates knowledge gained during a long-term U.S. Geological Survey investigation of the volcanic field, done in part because of its extensive history of mining. The investigation also was done to provide framework geologic knowledge suitable for defining geologic and hydrologic hazards, for locating hydrologic and mineral resources, and for an understanding of geologic processes in the area. A previous geologic map (Cunningham and others, 1983, U.S. Geological Survey Miscellaneous Investigations Series I-1430-A) covered the same area as this map but was published at 1:50,000 scale and is obsolete due to new data. This new geologic map of the central Marysvale field, here published as U.S. Geological Survey Geologic Investigations Series I-2645-A, is accompanied by gravity and aeromagnetic maps of the same area and the same scale (Campbell and others, 1999, U.S. Geological Survey Geologic Investigations Series I-2645-B).