A magnetic investigation of the Round Mountain plug, Castle Valley, Grand County, Utah

A magnetic survey was made in Castle Valley, Grand County, Utah, to determine if the Round Mountain plug was fed laterally from the La Sal Mountains or vertically from a source at depth. Additional measurements were made around the exposure of igneous rock to obtain the shape of the plug at depth. No indication of a buried lateral igneous feeder was detected on the magnetic profileso The magnetic contour map showed that the plug was much larger than indicated by the diorite porphyry outcrop, and that the buried part of the plug southeast of Round Mountain has a higher magnetic susceptibility than the diorite outcrop. Theoretical anomalies, calculated using the susceptibility of the diorite outcrop, indicate that a lateral feeder at a depth of greater than 200 feet could not be detected. The size and shape of the magnetic anomaly as shown on the contour map suggest that the plug was fed from a source at depth.