North Sister is the most rugged and considered the hardest climb of the Three Sisters in Central Oregon. It also could be considered one of the hardest of the Cascades volcanoes when comparing "standard" routes. It's the oldest and least climbed of the Three Sisters. First ascent was by H. H. Prouty in 1910 for which the summit pinnacle is named. Originally thought to be over 11,000 feet, it has eroded and is basically a large pile of loose volcanic rock. There are two pinnacles at it's summit and many gendarmes. There is also lots of loose rock and rockfall.