The majority of the rocks forming the mountains of the Peace Park are the result of the deposition of sediments into an ancient inland sea that existed over 1600 million years ago during the middle Proterozoic Era. The ancient Belt Sea covered parts of present-day eastern Washington, northern Idaho, western Montana, and nearby areas in Canada. During the period of active deposition over 18,000 feet (5500 m) of sediment eroded from nearby highlands and were carried into the sea. Accumulation of sediment subsequently resulted in downwarping of the sea floor. Also, over time and as environmental conditions varied, a variety of different materials were eroded and washed into the Belt Sea.
middle Proterozoic Era. Proterozoic Proterozoic Era.
middle Proterozoic Era. Proterozoic Proterozoic Era.