Rattlesnake Knoll is a small, isolated 30-meter-high mound of igneous breccia in the center of Spring Valley, White Pine County, Nevada. There is a small gravity anomaly associated with the knoll which, when combined with an initial, limited ground magnetic survey, indicates that rocks of the knoll probably extend northward in the subsurface. To explore this possibility, a 16-kilometer ground magnetic traverse was conducted in 2006 mainly along U.S. Route6/50, just north of the knoll.Magnetic data were obtained using a portable cesium vapor magnetometer integrated with a differential GPS receiver. The magnetometer was mounted on a non-magnetic aluminum fame and towed behind a vehicle, with measurements taken at 1-second intervals.