The lands surrounding the lake are part of the Canadian Shield, one of the largest single exposure of Precambrian rocks in the world which were formed after the Earth's crust cooled. Part of Lake Temagami lies in the Temagami Magnetic Anomaly, an egg shaped geologic structure stretching from Lake Wanapitei in the west to Bear Island. It has striking similarities to the Sudbury Basin, which is one of the richest mining camps in the world. The hills in the Temagami area are remnants of the oldest mountain ranges in North America, that date back to the Precambrian era. These enormous mountains were taller than any that exist today. The uplifting was accomplished as enormous pressure caused the earth to buckle in a process called folding. Other processes, such as volcanic activity and geologic faulting in which the earth cracks open also contributed to the formation of these mountains. Over millions of years, these enormous mountains were gradually eroded to the land as we know it today in Temagami.