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Aeromagnetic map of the Mokelumne Wilderness and contiguous Rare II further planning areas, central Sierra Nevada, California

Miscellaneous Field Studies Map 1201-B

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Abstract

The aeromagnetic map consists of parts of two surveys flown at an altitude of 300 m above the average ground surface. One survey (west park of the map_ centered over the Mokelumne Wilderness was flowing in a northeast-southwest direction along slight lines spaced at a horizontal interval of about 800 m (U>S> Geological Survey, 1979b). The survey to the east is part of a regional survey flown in an east-west direction along flight lines spaced at an interval of about 1,600 m (U.S. Geological Survey, 1979a). The join of the aeromagnetic contours along the border between the two surveys is generally conformable. The contour datum of the eastern regional survey, however, is about 650 nT (nanotesla) lower than the Mokelumne Wilderness survey because of difference in data reduction.


The aeromagnetic pattern reflects variations of magnetization within the underlying rocks, but the pattern is complicated by strong topographic effects. That is, magnetic anomaly maxima tend to occur over ridges and hilltops and minima over canyons and depressions. The topographic effect exists mostly because a constant ground clearance could not be maintained at normal aircraft speeds in this area of rugged topographic relief. The recorded flight altitude varied from 30 m to nearly 1,500 m above the ground with local changes that approard 1,000 m in distances of less than 5,000 m.


Four magnetic anomalies that can be related to geologic features are discusses., Magnetic highs or lows cause by topography are not discussed.

Geospatial Extents

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Aeromagnetic map of the Mokelumne Wilderness and contiguous Rare II further planning areas, central Sierra Nevada, California
Series title:
Miscellaneous Field Studies Map
Series number:
1201
Chapter:
B
Year Published:
1981
Language:
English
Publisher:
U.S. Geological Survey
Publisher location:
Reston, VA
Description:
Map: 37.01 x 33.97 inches
Country:
United States
State:
California
Other Geospatial:
Sierra Nevada
Datum:
National Geodetic Vertical Datum of 1929
Scale:
62500