A major time period when sandstone along with other sedimentary rocks in Minnesota were deposited was during the early Paleozoic era (about 500 million years ago). At that time, Minnesota was near the equator, and shallow seas covered most of the state. Sediment eroded from upland areas was transported to the seashore, and the coarser sediment eventually formed the sandstones seen today in southern Minnesota (above). Some of these sandstones are so poorly cemented that the grains can be rubbed off with your finger (below). As the sandstone is eroded, piles of clean quartz sand are formed.

(from Mossler, J.H., 1999, Geology of the Root River State Trail Area, southeastern Minnesota, Minnesota Geological Survey, Educational Series-10)