Regional geologic structures in the San Francisco
Mountains vicinity, southwestern Utah, are investigated
using aeromagnetic and gravimetric data.
Aeromagnetic data indicate a buried Tertiary
pluton whose north boundary runs east to west across
the study area and which extends beyond the coverage
of the aeromagnetic map to the east, south and west.
Local cupolas extend upward from the main igneous
body. A three-dimensional model is developed with a
digital computer for the distribution of the magnetic
rocks in the area. These model studies show that the
pluton is tabular, about 5 miles thick and has a nearvertical
and linear north edge which may have resulted
from the structural control exerted by an east-west
trending fault zone.
The Bouguer gravity anomalies reflect horst and
graben structures typical of the Basin and Range
Province and indicate a density contrast of + .10 grams
per ~c is associated with the local intrusive cupolas.
Three interpretive east-west geologic cross sections are
developed which reproduce observed residual gravity
The regional gravity data are interpreted to show
the effect of three regional structures:
1. An underlying intrusive body.
2. An east-west fault zone bounding the intrusive
body on the north.
3. A continuation of Basin and Range structure
at depths exceeding two miles.