Lichen, small organisms growing on spoils rocks, may prove useful in providing a relative age by which one spoil pile may be compared to another. By using the average growth rate of lichen, correlated with maximum size and cover in each spoils pile, a rough determination of how long ago the spoils were deposited may be determined. This lichen measures about 5 inches (13 cm), indicating the rock may have been dumped in this spot more than 200 years ago. Photo by Chris Caran.