The answer is C. Gulch.
A cliff is a steep, vertical or overhanging rock face. A canyon is a deep, narrow valley with steep sides, often carved by a river. A gorge is a deep, narrow valley with steep sides, often with a stream or river running through it. A ravine is a long, narrow valley with steep sides, often with a stream or river running through it.
A gulch is a small, narrow valley with steep sides, often with a stream or river running through it. Gulches are typically much smaller than canyons, gorges, and ravines. They are also typically less well-defined, with less distinct boundaries between the valley and the surrounding land.
Gulch is the only option that is not a type of valley. The other options are all types of valleys, with varying degrees of depth and steepness.