Long Knife Peak is a 9,789-foot mountain in Glacier National Park's Clark Range, with its main summit in the United States and much of its slopes extending into British Columbia near the international border. Rising more than a vertical mile above Upper Kintla Lake, it has strikingly steep local relief. Set on an east-west ridgeline mapped as the Boundary Mountains, it and nearby peak 8864 form the northernmost named high ground in the contiguous United States above 8,000 feet. Long Knife Peak is also the northernmost peak and land area in the contiguous United States above 9,000 feet, in a severe alpine subarctic environment with intensely cold, exposed conditions.