Pinnacle Mountain is an 8,400-foot granitic massif in Washington’s North Cascades, within the Glacier Peak Wilderness and Wenatchee National Forest. Ranked among the highest summits in the Chelan Mountains and the state, it rises above a rugged landscape of sharp ridges, craggy peaks, and deep glacial valleys. Its runoff feeds both the Entiat and Chelan River basins, marking an important divide in the surrounding high country. The mountain is made chiefly of granodiorite and hornblende quartz diorite of the Cardinal Peak pluton, and its setting reflects the North Cascades’ formation through terrane accretion, uplift, faulting, volcanism, and repeated Pleistocene glaciation.