In a wilderness setting, rocky outcroppings often have areas that often provide suitable areas for use as temporary shelters. They quite often will be found on higher ground and can provide you with protection from the elements.
The above picture shows a small cave-like area in a rocky outcropping. Just be sure to check that there aren't any current residents before making it a temporary shelter. Natural shelters give you the advantage of not having to use valuable resources to build a shelter. This enables you to save a substantial amount of time and effort by using natural forms of shelter.
Got river shelter?
Staying above the water line!