Ground surveying in Surprise Valley, Cedarville, California, United States. U.S. Geological Survey researcher Noah Athens secures a magnetometer pack onto Stanford graduate student Melissa Pandika, who blogged the team’s first year’s research for USGS in Surprise Valley, Modoc County, Calif., in 2012. Traditionally, magnetometric surveying has been done on foot or by all-terrain vehicle, and the Surprise Valley team’s aerial data is still ground-truthed this way. However, human-powered ground surveying methods are time-consuming and less precise than aerial surveys, and cannot be performed on dangerous or inaccessible ground.