The structure of Underwood Prairie is a series of small, undulating gravel knolls that are part of the Kaneville Esker, Illinois' longest esker, that was deposited here between 10,000 and 20,000 years ago. It is believed that eskers were formed by glacial debris washing across the massive ice sheets, into sinuous cracks or chasms in the ice, which later melted, leaving this wandering, linear imprint on the landscape (from Kane County Forest Preserve District).