The volcano is of Pliocene age and was active between 4 million years ago and 70,000 years ago; radiometric dating has yielded ages of 3.97 million years for rocks at the base of Mount Rittmann and 240,000 ± 200,000, 170,000 ± 20,000 and 70,000 ± 20,000 years ago for lava flows.