A glacially eroded valley. In mountainous regions rivers tend to carve out valleys with narrow bottoms, or V-shaped valleys. When alpine
glaciers flow through these pre-existing valleys, the glaciers reshape the valley and widen the valley bottom. The result is a valley shaped
like a parabola or a trough or a capital letter U (U-shaped valley).
Photo: R. Schukar. Used with permission.
The photo shows the glacial trough (or U-shaped valley) currently occupied by the Saint Mary River in Glacier National Park. Although no one
may have seen the glacier when it filled this valley, you can tell that the valley was shaped by a glacier and not by the Saint Mary River
simply based on the shape of the valley. In the photo, you are looking toward the northeast. On the map, north is toward the top. The wide
spacing of the contour lines on the map reveals the relatively flat floor of the valley while the more closely spaced contour lines along
the sides of the valley show the steeper valley walls.