The mounds, located in Afton Township, east of Mound Prairie Cemetery on Highway 18 (old Highway 95) are composed of bedrock. Bedrock is any solid rock mass, either at the surface of underlying such surface deposits, as glacial drift. Originally they were laid down by epicontinental seas covering North America in the Lower Ordivician, Lower Paleozoic Era, millions of years ago. They are composed of marine sediments in pre-glacial era; few fossils would be located there. The hills are capped with limestone that is resistant to erosion. However, the surrounding loose sand and gravel sides have eroded from the hillsides of the caps by action of local water run-off and at present geological scouring about 10,000 years ago during the last glacial action. On Highway 94 west of the St. Croix River is a selica or quartz possessing the same sand that originally surrounded the Bissell Mounds. The mounds are named for the family that lived near them in 1842-50. The first traveled road in Woodbury was from Stillwater to St. Paul via the Bissell Mounds. The mounds are 3 singular mounds of different sizes, occupying from 1/2 to 1/4 acre, situated on high ridges 40 to 50 ft. high.