 The county's highest point is Cache Peak at an elevation of above sea level in the Albion Mountains, and the lowest is Milner Lake, a reservoir on the Snake River, at .The northern half of the county is part of the Magic Valley region of the Snake River Plain, and numerous mountain ranges extend north from the southern boundary and diminish as they approach the river, which flows from east to west.The Silent City of Rocks National Reserve, containing exposed granitic batholith as old as 2.5 billion years, is located in the southern part of the county.