How were the okanogan highlands formed?

a. by subduction, which caused huge folds in earths surface

b. as a result of retreating glaciers carving great valleys into the earth

c. when molten rock from under the earth approached the surface

d. when the collision of volcanic island chains and ocean rocks formed new earth

The correct answer is:

a. by subduction, which caused huge folds in Earth's surface.

The Okanogan Highlands have been formed by the collision of the Pacific plate and the North American plate. The Pacific plate is subduction bellow the North American plate, and that cause the lifting up of the land in close proximity to the plate boundary. Over time, the Okanogan Highlands were formed, alongside the likes of the Cascades and the Rockies, all in the same process. The pressure between the two plates also caused a lot cracks and adjustments into the crust, and that resulted in the formation of huge folds as well in this highland area.