Before a lake and dam filled the valley, an ancient stream flowing from the north, now known as Rock Gap Run, slowly cut through rising sandstone bedrock that eventually became Evitts Mountain, creating Rocky Gap Gorge and numerous rock shelters above the stream. Over thousands of years, Native American Indians used these overhanging stone ledges as temporary shelters. Their deep history in this region is outlined in a timeline from the Contact Period of the last 500 years, when Euro-Americans first came into the area to trade with Indians, through the Woodland Period of 3,000 years, when people developed agriculture, grew corn, beans, and squash, introduced ceramic pottery and the bow and arrow, and began to live in villages. Before that came the 6,000-year Archaic Period, when the climate changed from cool and dry to warm and wetter, hardwood forests replaced spruce forests, swamps formed, and people lived in small hamlets as a hunting and gathering society that used the spearthrower as its main hunting weapon and foraged nuts, berries, and roots. Earlier still was the 3,000-year Paleo-Indian Period, when small, semi-nomadic family groups hunted large and small game, collected wild plants for food, lived in a cool and humid environment like northern Canada today, and made high-quality spear points while mammoths, mastodons, elk, moose, and caribou roamed the open terrain as the last Ice Age glacier retreated north out of Pennsylvania. Little is known of the Pre-Clovis Period, but sites across North America, including one as close as the Pittsburgh region, indicate Indian occupation was much older than 12,000 years ago, when archaeologists once believed Native Americans first entered from Asia.