A magnetic survey of Sand Canyon for placer deposits, San Gabriel Mountains, California

• Main Author: Dehlinger, Peter
• Format: Others
• Published: 1943
• Online Access: https://thesis.library.caltech.edu/5576/1/Dehlinger_p_1943.pdf; https://thesis.library.caltech.edu/5576/2/Dehlinger_p_1943_plate.PDF; Dehlinger, Peter (1943) A magnetic survey of Sand Canyon for placer deposits, San Gabriel Mountains, California. Master's thesis, California Institute of Technology. doi:10.7907/CPV2-4136. https://resolver.caltech.edu/CaltechTHESIS:03052010-085246594 <https://resolver.caltech.edu/CaltechTHESIS:03052010-085246594>

A magnetic survey was made in Sand Canyon, which is in the northwestern part of the San Gabriel Mountains, the object being to locate possible placer deposits. The bedrock in this area is an iron rich igneous rock which has been intruded by numerous dikes. The stream gravels consist of large boulders interspersed with highly magnetic sands. Over 200 stations were involved in the survey in which vertical magnetic intensity was measured using a Schmidt-type vertical magnetometer. Magnetic anomalies found were so large that all instrument corrections were ignored. Results of the survey show that the magnetic intensity readings are due to both the basement and the gravels, though the gravels have a greater effect. The location of the largest anomalies, thus the most probable placers, is at the eastern end of the area. Downstream from this site the intensity decreases rather uniformly; upstream it decreases very sharply where the canyon narrows suddenly. Geologically, this is the expected picture. It is thought that a fault has been located, which strikes up the canyon, but this has not been confirmed by surface evidence. Data and profiles of the traverses, and a detailed map of the magnetic intensities of the region are included in this paper.