The Flattops comprise the northern extent
of the White River Plateau. Uplift began approximately 52
million years ago. Three periods of volcanic activity
followed the uplift, between 2.4 and 7.5 million years ago.
Pleistocene and possibly some early Holocene glaciation
occurred approximately 13,000 to 17,400 years ago. This left
many glacial lakes and U-shaped valleys. Elevation ranges
from 8700 feet to 12,347 feet.