English: Magnetic field gradient image of a council circle located on a Great Bend aspect archaeological site in central Kansas. The data reveal a complex earthen works feature with numerous internal and external features. The main feature appears to be some 60 meters in diameter and may be described as a complex circular or oval shape with four or more lobes. The outer limits of the feature appear as concentric bands of positive and negative signal. There are approximately four to five of these bands. It is not clear whether these bands represent re-building events, contraction/expansion of the structure over time, or are part of the original structure plan. The central portion of the structure is devoid of this banding, but does contain numerous anomalies that appear to represent internal archaeological features. Many anomalies are visible outside the main structure as well. These anomalies appear to represent archaeological features external to the council circle.

Magnetic survey is one of several non-invasive mapping methods commonly used in the discipline of archaeological geophysics.

Source: http://www.archaeophysics.com/sharps/