The above image is from the Alpine Quadrangle in Montana.  Toward the bottom of the image and bending to the right is a large U-shaped Valley characteristic of glaciated terrain.  Another glacial feature, a hanging valley, can be observed in the upper left hand side of the image.  Imagine the U-shaped Valley completely filled with glacial ice.  The ice from the hanging valley could then enter the main glacier at a high level relative to the floor of the U-shaped valley.  During glaciation, the hanging valley supplied more ice to the main glacier at this higher level.  After the ice melted, a high U-shaped, scoured valley was left well above the main valley floor.

In this case the hanging valley's cirque is nearby and the tarn's within the base of the cirque are visible in both images.  The image below is a view from the hanging valley down to the main valley.  In both photos notice the large elevation change between the hanging valley's floor and the main valley's floor.