Mount Formidable is a mountain in the North Cascades of Skagit County, in Washington state.

[1]: 265–267  It was named by early mountaineer Herman Ulrichs in 1935 because of the rugged appearance of its north face.

The surrounding area is part of the Pacific temperate rainforests ecoregion, and lower elevations are densely vegetated.

[5] More specifically, the immediate area surrounding Mount Formidable (i.e., within ten miles), is mainly composed of granitic rocks that are Mesozoic in age, and schist that dates from the late paleozoic.

[6] Mount Formidable itself is likely composed of originally igneous rocks that formed in the Triassic and were metamorphorphized in the Late Cretaceous.