"Frenchman Mountain Dolostone named after 500 million years"
Geologists have identified and named a previously unexplored 500 million-year-old rock layer in the Grand Canyon, calling it the Frenchman Mountain Dolostone (FMD). The FMD is over 1,200 feet thick at Frenchman Mountain, but it thins dramatically toward the east. The portions exposed within the Grand Canyon range in thickness from nearly 400 feet near the "West Rim" Skywalk to less than 100 feet in Marble Canyon, in the eastern part of Grand Canyon National Park. The FMD is the first new formation to be named in the canyon since 1985 when the Surprise Canyon Formation was named.