Geologic Map of the Central Marysvale Volcanic Field, Southwestern Utah

This database was developed to improve upon previous mapping in the central
Marysvale volcanic field and compile older mapping at a consistent scale. This
area is an important mining district, and a regional understanding of the
geology and mineral deposits will assist in understanding genesis of deposits
and in exploration for new deposits. The area is also an important part of the
transition zone between the Colorado Plateau to the east and the Great Basin to
the west. This tectonically significant province may hold keys to the style
and mechanisms of continent-scale deformation in the Western United States.

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the same area as this map but was published at 1:50,000 scale and is obsolete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).