The soil is silty, clay loam formed from sandstone, sediment, and igneous rocks.

[5] Streams flowing south from the Calapooyas into the North Umpqua River include Steamboat, Canton, and Rock creeks, while Calapooya Creek flows west from the divide into the Umpqua main stem.

Streams flowing north or east into the Middle Fork Willamette River include Tumblebug, Staley, Coal, and Packard creeks.

In the 19th century, it separated the tribal domains of the Kalapuya and Umpqua tribes of Native Americans.

The Applegate Trail, blazed in the late 1840s, provided the first reliable path for white settlement through the western end of the mountains.