Answer:
A lot of factors over time might have led to the formation of Death Valley.
In geological terms, it is a graben. A graben is a depressed block of the crust of a planet bordered by parallel faults. It is the sinking of the bedrock lying between parallel, uplifted, tilt-block mountain ranges. Grabens occur side-by-side with horsts. These structure indicate tensional forces and crustal stretching.
Other factors such as volcanic activities, erosion, evaporation of lakes during the Ice Ages and so on.
Even right now, it still undergoes geological changes.
