Pro Tip: Soil Creep
Forests can be pretty creepy at times. Soil creepy, that is. When you come across trees on a slope that have bends at the base of their trunks, chances are you're seeing the effect of the sum of numerous momentary movements of material on that slope caused by gravity.
This process is called geotropism (or gravitropism). This simply means the shoot of the tree grew at an angle caused by the hill sliding. As it established its root system, the stem grew upward (against gravity), thereby leaving a nice bend in the trunk.
Filmed at Hannegan Pass in the North Cascades, Washington.