Q Applying textures

Hey

I'm trying to figure out how you would go about applying a certain texture to every surface that has a certain coordinate. Lets say you have a large terrain with a lot of raised stalagmite formations and you want to apply one texture to the stalagmites and another to the plane they are on. I assume you can somehow apply textures to coordinates I just have no idea how

Any help would be awesome!

 

I don't know if my explanation of what I'm looking for is unclear, so I'll try with other words.
Can you put a texture on all flat surfaces that has a certain height?
The picture shows a sandy like texture and a rough rock like texture (the dark texture). The terrain is made using the terrain in unity 3d and just raising certain points like the wall in the picture. it has a height of 4 units and has a plane top surface. it is raised up from the terrain plane and I would like to put the rough rock texture on all walls.
So I thought if you can just force a texture on all surfaces of the terrain plane that has certain coordinates it would save a lot of time. I imagine that making the rough rock texture the default texture and making forcing the sandy like texture on plane that the "wall" is standing on would be easiest since it is a plane and the wall is kind of complex.
I just have no idea if this is actually something easy to do or where to begin. I would love some help with this as it would save me hours and also making future terrains much easier.

 

I tried to change to picture I had uploaded to one with a better perspective but the spam filter didn't approve of that, I don't know if it just doesn't like editing since it is the same picture as below.