In geography, a spur is a piece of land jutting into a river or stream or a ridge descending from mountains into a valley. Spurs are formed from erosion over time and frequently divide tributaries or valleys.
Types of spurs include interlocking spurs and truncated spurs. Interlocking spurs are alternating spurs often formed near the upper part of a river or stream where vertical erosion impacts the flow of water. In this situation, water flows in one direction until vertical erosion pushes it toward the opposite direction. As the flow switches back and forth, spurs form on alternating sides of the river or stream. Truncated spurs are interlocking spurs affected by glaciation. In a river valley subject to glaciation, the direct movement of the glacier removes the tips of the spurs, reducing the amount of land protruding into the river.