Horse Mountain is a 4,686-foot summit in Lake County within Mendocino National Forest, northwest of Clear Lake in the Middle Creek drainage basin. Set between nearby branches of Middle Creek and the Eel River system, its waters ultimately flow toward the Sacramento River, giving it a notable position near a divide between North Coast watersheds. With 1,126 feet of prominence and 9.13 miles of isolation, it stands out clearly from surrounding ridges. The mountain is mostly forested, though its summit has been cleared, and it remains part of the rugged public-land landscape used for hiking, all-terrain vehicles, and dirt bikes.