Geophysical Unit of Menlo Park, Calif. (GUMP)
An important objective of geologic mapping is to project surficial structures and stratigraphy into the subsurface. Geophysical data and analysis are useful tools for achieving this objective. This aeromagnetic anomaly map provides a three-dimensional perspective to the geologic mapping of the Los Angeles 30 by 60 minute quadrangle. Aeromagnetic maps show the distribution of magnetic rocks, primarily those containing magnetite (Blakely, 1995). In the Los Angeles quadrangle, the magnetic sources are Tertiary and Mesozoic igneous rocks and Precambrian crystalline rocks. Aeromagnetic anomalies mark abrupt spatial contrasts in magnetization that can be attributed to lithologic boundaries, perhaps caused by faulting of these rocks or by intrusive contacts. This aeromagnetic map overlain on geology, with information from wells and other geophysical data, provides constraints on the subsurface geology by allowing us to trace faults beneath surficial cover and estimate fault dip and offset. This map supersedes Langenheim and Jachens (1997) because of its digital form and the added value of overlaying the magnetic data on a geologic base. The geologic base for this map is from Yerkes and Campbell (2005); some of their subunits have been merged into one on this map.
Download the map with text as a ~61" x 34" PDF file (10.6 MB).
For more about gravity and magnetic data and methods, visit the Geophysical Unit Menlo Park website
For more about geologic mapping in Southern California.
For more about earthquake studies in Southern California, visit the USGS Pasadena Field Office
For questions about the content of this report, contact Vicki Langenheim
This report supercedes U.S. Geological Survey Open-File Report 97-162 (1997)
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