Gardeners from northern New Castle County should be grateful that the glaciers stopped their descent at the Delaware Water Gap about 100,000 years ago.
Had they continued on down, they would've scraped off the soil and left us with huge swaths of exposed rock and thin, meager soil as they did in New England.
Instead, we have regolith, a rich combination of weathered rock and acidic soil typical of the Appalachian Piedmont province.
As the vegetation dies back and garden beds become bare, it's easy to notice that rocks are everywhere, with each winter seemingly spawning a new crop.
"In the Piedmont, the rocks you find in your yard are just bits and pieces of weathered rock, and you're most likely to find quartz-rich rocks because quartz is hard and the most common mineral," says William "Sandy" Schenck, a geologist and associate professor of geology at the University of Delaware.
Weathered rock, known as saprolite, yields up fieldstone. "Fieldstone is a common name for rocks farmers found in their fields; [the term] doesn't have anything to do with geology," he says.
The colors of fieldstone reflect the minerals in the rock, with iron creating the signature reddish stain.
"Most of the rock in the Delaware Piedmont has a lot of iron in it, which tends to make our soil red and lightly acidic," says Schenck, adding that plants generally do well