Gullies are formed by branches of narrow valleys.

They feature V-shaped cross sections with steep slopes that are alternately bare or rich in greenery.

These groups of erosion furrows are either fan-shaped or present in short, sharp strokes. Gully formation requires a substratum of clay or marly soil eroded by meteoric water.

At the bottom of gullies we often find marshy depressions that contain sullage dragged down by water from clay deposits above.