Most glacial valleys were originally cut by stream erosion and then widened as the glacier eroded the valley. As the glacier widened and straightened the valley, the fronts of ridges which extended into the valley were removed or truncated.
Half Dome Gilluly, J., A. C. Waters, and A. O. Woodford.
Principles of Geology.
W. H. Freeman and Company, San Francisco, 1975.