 North of the South Fork Payette River and east of the North Fork Payette River , the forest is part of the Salmon River Mountains , which extend north and east outside the forest 's boundaries . The South Fork Salmon River Range and the North Fork Range are <unk> of the Salmon River Mountains within Boise National Forest . The Boise Mountains cover much of the southern portion of the forest and contain the forest 's highest point , Steel Mountain , but the range 's highest point , Two Point Mountain , lies outside of the forest 's boundary . The Trinity Mountains are a <unk> in southeastern part of the Boise Mountains that reach their peak at 9 @,@ 451 feet ( 2 @,@ 881 m ) on Trinity Mountain . The westernmost portion of the forest south and west of Lake Cascade are part of the West Mountains , which reach their highest point at 8 @,@ 320 feet ( 2 @,@ 540 m ) on <unk> Mountain . The <unk> Mountains are a smaller range on the forest 's southern border that run northwest to southeast . 
