Between the Pleistocene epoch and the last glacial period, the lake occupied the entire Mexico Valley. Lake Texcoco reached its maximum extent 11,000 years ago with a size of about and over deep. When the lake's water level fell it created several paleo-lakes that would connect with each other from time to time. At the north in the modern community of San Miguel Tocuilla there is a great paleontological field, with a great amount of pleistocenic fauna. The Lake was primarily fed by snowmelt and rain runoff when the Mexico Valley had a temperate climate. Between 11,000 and 6,000 years ago, the climate naturally warmed and snowfall in central Mexico became less prevalent. This caused the water level of the lake to drop over the next several millennia. Remnants of the ancient shoreline that Lake Texcoco had from the last glacial period can be seen on some slopes of Mount Tlaloc as well as mountains west of Mexico City. The disarticulated remains of seven Columbian mammoths dated between 10,220 ± 75 and 12,615 ± 95 years (BP) were found, suggesting human presence. It is believed that the lake disappeared and re-formed at least 10 times in the last 30,000 years.