Explanation of the Earth's gravitational field, emphasizing how USGS scientists measure gravity and portray these measurements on maps. Explains terminology of gravity anomaly maps and their relationship to the rock types and other geologic features.
Explanation of the Earth's magnetic field and how USGS measures it. Defines magnetic anomaly, induced and remanent magnetism in rocks, and describes magnetic anomaly maps.
Report describing detailed interpretation of geophysical survey data to draw inferences about subsurface geologic features and likely consequences for the hydrogeologic system.