The Salt Lake Valley is fed by seven streams from the surrounding mountains. All the runoff water eventually ends in the Great Salt Lake, which has no outlet. The mountains rise precipitously from the relatively flat valley surfaces, indicating their comparatively youthful formation. The county has a total area of , of which is land and (8.1%) is water. It is the fifth-smallest county in Utah by area. The county borders on the Great Salt Lake and is traversed by the north-flowing Jordan River.