O'Sullivan Peak, also called Sunrise Peak, is an 11,275-foot mountain in Utah’s Wasatch Range southeast of Salt Lake City, within the Twin Peaks Wilderness of the Wasatch–Cache National Forest. Rising sharply above Little Cottonwood Canyon, it gains 4,475 feet in just 1.4 miles and stands prominently between Little and Big Cottonwood canyons in the central Wasatch skyline. Runoff from its south slope drains to Little Cottonwood Creek, while the north side feeds Big Cottonwood Creek, both flowing to the Jordan River. Its official name, adopted in 1978, honors Timothy H. O'Sullivan, a Civil War and western frontier photographer who worked in the region.