Gunter Faure and Jack Kovach, using Rb-Sr dating, determined the age to be 1635 ±24 million years old [REF].
The Penokean Mountain Range formed in the Penokean orogeny 1880 to 1830 million years ago, when an oceanic island arc called the Pembine-Wausau terrane collided with the southern margin of the Superior craton [REF].