Started off with the main render from Unreal

Added an image of an evening sky, using a paint brush to make it fit the lighting of the Unreal render

Added clouds

Added canyons as which were individually rendered in Unreal

Added paint to the cacti and rocks in the foreground

Added some paint to the canyons and added some dust in the distance

Took those layers to After Effects, made some final adjustments and then tracked those layers to follow the camera