One of the earliest signs of fall comes in late August, when dogwood and black gum leaves, green since spring, begin to show the salmon and maroon colors they are soon to be, and when Virginia creeper vines, hidden in the canopy all summer, suddenly redden, revealing their upward windings through the tallest trees. But the surest sign of fall for me lies not overhead but underfoot, in the form of acorns lying on our trails.