| The National Park Service, Photographer: P. Brease. | Description: GLACIAL ERRATICS This house-sized granite boulder (notice the person below on the right for scale) was plucked from bedrock 58 km to the southeast and left on this ridge overlooking Denali Park Headquarters by an ice advance named the Brown Glaciation. The Brown Glaciation may have been the maximum ice advance in central Alaska during the Pleistocene Epoch (10,000 to 2 million years ago). However, even this maximum expansion of glacier ice did not cover the interior basin of Alaska (between the Alaska Range and the Brooks Range) which remained an arid grassy step that was a corridor for migration of plants, animals, and humans from Asia to North America. |