I have been tasked with proof reading before publication a Russian paper that has been translated into basic English and am searching for a word to describe the area of a glacial valley where the valley sides transitions into the valley floor?
Others may know if there is specific term for what you are asking. In case there isn't the following may help.
The walls of a valley are slopes - some are steeply dipping while others are shallow dipping. The top of a slope, whether natural or engineered, is called the crest of the slope and the bottom of a slope, where it meets the floor is called the toe of the slope.
Where the toe is not sharply defined and the slope transitions into the floor I would call that a transition toe.
The other term than is sometime used, instead of toe, in reference to continental slopes is foot.