Observatory Hill Mound Group is a Native American archaeological site on the University of Wisconsin–Madison campus that preserves two surviving effigy mounds, one shaped like a bird and the other like a double-tailed turtle or water spirit. Built between 650 and 1200 A.D. by Late Woodland people, the earthworks are part of the tradition that created effigy mounds across Wisconsin. The group was once larger, including a panther effigy and a linear mound, but those were destroyed in the twentieth century. The surviving mounds were listed on the National Register of Historic Places on March 31, 2004, for their significance within Wisconsin’s mound-building heritage.