Rock shelter
shallow cave-like opening at the base of a bluff or cliff
A rock shelter is a shallow cave-like opening at the bottom of a cliff. Rock shelters form because a rock stratum that does not erode has formed a cliff. But a weaker stratum, that erodes a lot is under the resistant stratum. As it erodes it creates an opening at the bottom of the cliff.
![](http://up.wiki.x.io/wikipedia/commons/thumb/3/3f/Rock_shelter_Papula.jpg/220px-Rock_shelter_Papula.jpg)