Northeastern Washington County's earliest known inhabitants were pre-Columbian Mound Builders, who constructed effigy mounds in the area sometime between 650 CE and 1300 CE. They were semi-nomadic and survived by hunting, fishing, and gathering wild plants. They made pottery and constructed tools from bone, wood, stone, and occasionally copper. They built effigy mounds shaped like mammals, reptiles, birds and other creatures, both real and mythical, as well as conical, oval, and linear mounds, some of which contain human burials. Some mounds in the West Bend area were destroyed by white settlers to create farm fields, but several dozen survive and are listed on the National Register of Historic Places as the Washington County "Island" Effigy Mound District, which includes the Lizard Mound County Park site in nearby Farmington as well as several privately owned sites.