Just a tip to make the terrain follow the ramp perfectly: make a distance render from the ramp seen from the top. Use that render as a terrain and scale it so that it is just a very little bigger than the ramp. Then you can put some small erosion on the terrain (or whatever else you want it to look like) and you should be able to fit a bryce terrain right underneath the ramp. I think from this distance, and considering the terrain is mostly below the ramp, a 512 x 512 terrain should be more than enough (unless you want to render a huge resolution)