This might look like just a big rock, but it's actually a metate, or grinding stone. The waterworn, basalt-like rock could have come from glacial outwash. How can we tell it's a metate? The surface is broad, flat, and smoothed from being rubbed with a handheld stone (mano). The drawing shows a well-worn metate and mano, which would have been used for grinding corn or other materials. The metate in the photo is about 400-700 years old and was found at a precontact Oneota site in Onalaska, Wisconsin. The site had been stripped by heavy equipment that left light-colored, nearly parallel scrapes across the stone's surface. The darker, broken places at both ends represent much older damage. For more information on these important tools, link to watch MVAC's "Mano and Metate" video.