Mount Formidable is located on a spur ridge about half a mile west of the Cascade crest, between Cascade Pass and Dome Peak, and about a mile west of Spider Mountain. It is within the Marine west coast climatic zone, and experiences heavy snowfall as a result. The surrounding area is part of the Pacific temperate rainforest ecoregion, and lower elevations are densely vegetated.: The Middle Cascade Glacier, which drains into the Skagit River via the Cascade River, is on the north side of the mountain.: