The area is dominated by rugged glacier-covered mountains or glaciated mountains with deep V-shaped and U-shaped valleys that straddle the international boundary with Canada.
(The area; is dominated; by rugged glacier-covered mountains or glaciated mountains with deep V-shaped and U-shaped valleys) (deep V-shaped and U-shaped valleys; straddle; the international boundary with Canada)
The area deep V-shaped and U-shaped valleys
is dominated straddle
by rugged glacier-covered mountains or glaciated mountains with deep V-shaped and U-shaped valleys
the international boundary with Canada