Bridal Veil Falls, Yosemite.
A hanging valley is a tributary valley that ends high up the face of a larger main valley, possibly with a stream running through it and ending in a waterfall. Hanging valleys are usually associated with U-shaped valleys, and result from a tributary glacier having flowed into a glacier of larger volume. The main glacier eroded a deep U-shaped valley with nearly vertical sides while the tributary glacier, with a smaller volume of ice, made a shallower U-shaped valley. Since the surfaces of the glaciers were originally at the same elevation, the shallower valley appears to be hanging above the main valley.
A well known example is the hanging valley in Yosemite National Park over which Bridal Veil Falls plummets.