An interlocking spur is a natural geographical feature that occurs in the upper course of a river in which downward erosion is the dominant force determining the river's course. As a river wanders between banks that are far apart, the promontories of the hills tend to jut out into the river valley resulting in a staggered formation, interlocked together somewhat like the teeth of a zip. These promontories are referred to as interlocking spurs.
If the river valley is subsequently subject to glaciation, the glacier shears off the tips of the interlocking spurs, due to its straighter course, creating truncated spurs.
While similar in general appearance, the mechanism behind the formation of interlocking spurs is different to that behind meanders, which arise out of a combination of horizontal erosion and deposition.