MAGNETIC AND ELECTRICAL RESISTIVITY STUDIES OF THE CIRCLE MOUND EARTHWORK AT MOUNDS STATE PARK, ANDERSON, INDIANA

Geophysical surveys were conducted at Circle Mound at Mounds State Park, Anderson, IN. The primary purpose was to locate two entrance mounds described in an Indiana Geological Survey Report, Cox 1879. Circle Mound is a Woodland earthwork enclosure located along the east bank of the White River with a central platform at original ground level surrounded by a trench that is eight foot deep and a rim that is four foot high. It has an east facing entrance ramp and is approximately 150 ft by 240 ft with the length running east to west. The two entrance mounds were reported to be located north and south of the entrance. Magnetic and electrical resistivity surveys have been conducted at two different times. The original 1980 surveys were conducted on one-meter grid starting at the eastern rim to 20m east proceeding 20m north and south of the center. The magnetic data showed various anomalies throughout the grid with further research showing four of these to be rocks positioned by humans with apparent alignment to calendar events (Robinson, 1980). Two of these are found along the east-west centerline near 5E and 20E. The other two are found to the north and south approximately where the entrance mounds have been located. Both the magnetic and resistivity data show a pattern of highs and lows that are relatively symmetrical around the central E-W line. The recently collected data were measured on a grid running 30m east, 65-80m west, and 25m north and south. This enlarged the preexisting grid and includes the interior of the earthwork itself in the magnetic survey. Current resistivity and magnetic data, while similar, do not show as clear a symmetrical distinction for the southern mound due to excavation conducted following the first study. This helps to show that the symmetrical patterns were due to shallow changes in iron oxide and porosity that were within the range of excavations and that can be attributed to human activity associated with the mound builders.