About two-thirds of Cougar Mountain has experienced residential development, and is home to many neighborhood communities such as Lakemont.

The forested heart of the hill was officially preserved by King County in June 1983 as Cougar Mountain Regional Wildland Park.

Cougar Mountain was formed in the Miocene when tectonic forces folded western Washington along a northwest axis and created the Newcastle Anticline.

The anticline exposed earlier (Eocene to Oligocene) sedimentary and volcanic rocks that, due to erosion, now form the surface of Cougar Mountain.

[2] Cougar Mountain is part of the Eastern Puget Uplands level IV ecoregion, as defined by the EPA.