Glacial outwash is sand and gravel deposited by running water from the melting ice of a glacier. When rivers of melt water wash away at glacial till deposits, they carry the finer clay-sized materials away and leave behind thick outwash deposits of sand and gravel that concentrate in valleys. The glacial outwash then forms an outwash plain, known as a sandur, formed from the meltwater of glaciers. In southwestern Ohio, the melting of Ice Age glaciers filled many such valleys with hundreds of feet of sand and gravel. These deposits make excellent aquifers, or buried sources of groundwater. In Ohio, the largest of these aquifers is in the Great Miami-Mad River Valleys, which stretch between Bellefontaine and Cincinnati. The pen in the image on the right helps to show the size of a local deposit.

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Sandur at Wikipedia.org