I think it is in the spring stage of development.
The meteor that struck the Earth, and created the Grand Canyon. Was powerful enough to tilt the Earth’s axis.
Answer:
Rift valleys are Formed from either from the action of tensional forces in the crust or from the action of compressional forces!
And they move due to the force of gravity!
The block mountain (horst) is left standing higher above the sunken graben!