Landscape distortion,What would be the best way to produce distortion landscape ?

Hey ,

I want to generate this kind of landscape :

and to be able to distort them, flip them and scale them . I also want create them with a lot of realism and details . Like this guy from Unreal has been doing http://gkaradayi.com/ What would be the better way ? ( not the easiest way but the most accurate one ) Is HDRP a possibilty ? Wich assets would you recommend ?

Thanks you

Ps: I already check that landscape can't be rotated so I am looking for an alternative way