All three forks of the Kings River originate as snowmelt in the high Sierra Nevada mountains. The Middle and South Forks begin in Kings Canyon National Park, and join in the Monarch Wilderness (Sierra and Sequoia National Forests) to form the Kings River. The North Fork, which begins in the John Muir Wilderness of the Sierra National Forest, joins the Kings River further downstream near Pine Flat Lake, the only major reservoir on the river. Much of the upper Kings River consists of remote backcountry and wilderness areas, accessible only by non-motorized trails. The entire upper course of the Kings River is in Fresno County; in the Central Valley, the Kings River also flows through parts of Tulare County and Kings County.