The Archaic–Early Basketmaker Era (7000–1500 BCE) was an Archaic cultural period of ancestors to the Ancient Pueblo People. They were distinguished from other Archaic people of the Southwest by their basketry which was used to gather and store food. They became reliant on wild seeds, grasses, nuts, and fruit for food and changed their movement patterns and lifestyle by maximizing the edible wild food and small game within a geographical region. Manos and metates began to be used to process seeds and nuts. With the extinction of megafauna, hunters adapted their tools, using spears with smaller projectile points and then atlatl and darts. Simple dwellings made of wood, brush and earth provided shelter. The Archaic Basketmaker Era is followed by the Early Basketmaker II Era. Hunter gatherer culture Holocene climate changes (beginning about 10,000 BCE) resulted in warmer and drier weather, a contributing factor in the extinction of megafauna, such as the mastodon and mammoth that were hunted by the preceding Paleo-Indians. Besides climate change, the large animals may have perished due to increased human population and their improved hunting techniques. By 6000 BCE two-thirds of all North American animals weighing more than 100 pounds were extinct and the bison antiquus was the only large animal to survive on the Great Plains. About 5000 BCE Holocene glacial runoff affected Colorado Plateau storm patterns which resulted in significant soil erosion. Between 2500 and 2000 BCE there was significant soil build up. When the climate became too arid to produce sufficient food, people relocated until the rate of precipitation increased. Over time there was an increase in drought-resistant plants and the plants that required regular watering did not survive. Woodlands of spruce and fir were replaced by juniper and pinyon trees in the northern Rio Grande valley. Further south, there were fewer juniper and pinyon trees. Both climatic changes resulted in human movement pattern changes to obtain food. The Paleo-Indian had a straightforward movement pattern: follow and hunt the big animals. The Archaic individuals followed a new pattern called "making the seasonal rounds" where they moved to familiar places based upon the growing seasons of plants, their major source of food. In the spring, summer and early fall women harvested seeds, nuts, fruit, grasses, juniper berries and mesquite beans. Any surplus food was stored for later use. Men hunted small game like rabbits using traps and snares. During the fall and winter