Mount Persis (Wikipedia) Mount Persis is a 5,464 ft summit located in Snohomish County, of Washington state. The mountain is part of the Cascade Range and is situated in the Mount Baker-Snoqualmie National Forest. The mountain was named for Persis Gunn, the wife of homesteader/miner Amos Gunn who started the nearby town of Index, Washington, and also named nearby Mount Index. Precipitation runoff from the mountain drains into tributaries of the Skykomish River. The rocks of Mount Persis are volcanic in origin and are considered amongst some of the earliest expressions of volcanism in the Cascade Mountain range in Washington.