The one good thing about the IC terrain system is that textures map quite uniformly, so that on slopes and such they don't stretch. This is from an iClone 5 project (rendered in IC6):



So it's pretty good for details.

Now a mountain is a different story because of the size, and you may have to trick it somehow. It depends also on whether the mountain is just in the background or needs to be climbed.

During the time that most films were done on the studio lot they had to come up with clever ways to emulate that mountain. I've been thinking for my own projects that something could be done by creating 360-degree backgrounds, perhaps even layers of them.

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You may not need a whole mountain. That will depend on your shot requirements. It is probable better to make a "mountainside" than a whole mountain. But using imported meshes and picture backdrops can go long way. Try using heightmap terrain for stuff the camera will be closer to. Only the heightmap terrain can use the 4 material splat map rendering, but you can tile that as much as you need for it to look nice up close.

You can also use forced perspective to make your distant mountain "huge". Just make the trees really small, or even use 2D grass with tree images.

Ironically, I have exactly the opposite issue with the heightmap terrain. It cannot scale smaller. ;)

EarthSculptor is very usefull for me and enought fot my need because I'm not making a game, so I didn't need to make full hirez terrain at large.
I suggest you to download the UDK 4 engine and download the free map with very large terrain. It's very instructive to see how to fake huge aera
with very low props as mountain.
In my exemple I use this eightmap i found on the web:



Then I use 4 mountains coming from UDK 4. There're only 1990 polygons and the texture is very professional and only 2k.





The result for huge mountains:

you can do this in blender with the landscape plugin and then paint it inside blender as well

did this long ago the plugin is still there and I use it from time to time so i know it still works.



I created this for use with the iclone 5 thingy which I was using at the time.   

you can easily adapt this to use the vertex method and take advantage of tesselation by using colours I would think for various heights and use the vertex thingy for displacement as well I suppose.   (yes as usual i am being highly technical.  I know this bothers a lot of people but its how i talk lol sorry :P)

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"You have brains in your head. You have feet in your shoes. You can steer yourself in any direction you choose. You're on your own, and you know what you know. And you are the guy who'll decide where to go."
                                                                                                                                                                                                                                                                                     Dr. Seuss

I'm going with a model of Mount Shasta created from a height map in Blender, then painting it up in Substance Painter. What I was really hoping for was a way to use substances similarly to how the default terrain uses the mask channels, but I haven't figured out a way, using separate materials on the mesh shows seams when using displacement, and I don't see a way to use an RGB mask when using a substance within iClone for a prop. But anyhow, painting in SP works well, pretty much total control and PBR ready. Thanks Rampa for clarifying about Earth Sculptor, I was under the impression that I could get more detailed maps from it, but then I would need my own mesh and then the mask layer wouldn't work anyhow. 

That said, regarding scale, I've found that scaling down the initial Speedtree before planting can help beef up the scale, and since I'm working from a height map, I could always load in the same heightmap and texture used to create my custom prop into the default terrain system, I haven't tested this much yet, but I'll be trying that today. 

EDIT: I just tried, I made a blank mask image for the mountain, the way the textures gets mapped doesn't give the same effect, but it actually looks pretty good the way the textures get blended. If I use the whole mesh just for the mountain scene and add meshes for any foreground shot, it should look pretty good I think. Anyhow, good to have options. The screen shot is with the minimized trees and default mesh.

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My system: i7 3770 Gtx1060 6GB

Looks pretty decent I try to not go nuts with detail for things that wont be seen close up its a waste of my pc resources & I like to save as much as possible.  I am very stingy and picky about my polygons and texture sizes for things like this.  :)

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"You have brains in your head. You have feet in your shoes. You can steer yourself in any direction you choose. You're on your own, and you know what you know. And you are the guy who'll decide where to go."
                                                                                                                                                                                                                                                                                     Dr. Seuss

I wonder if, just like we have colored maps to indicate various areas for clothing in CC, something similar could be added for using Substance for props. If that makes sense...:unsure:

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i made a freebie with a substance for that its on the forum.     Its just for texturing though and it uses a mesh.   I created the substance for it too for anyone to use.   Anyhow its possible to do this my examples dont use much blending but its all quite possible.   There were some bugs in iclone making it hard to use certain things from the substance designer (in that they simply were not working) and i never got back to it.. its possible they repaired the nodes that were causing it to crash but I dont know :)

I do a lot of stuff just to you know "expand my mind" or whatever but half the things I find are not that practical when making an actual video (too resource intensive) so I never get back to them because in the long run I tend to fall back on more practical things.    In the end I think its just better to make a low poly mesh in a pleasing shape and paint it so that it uses 1 or 2 materials with corresponding textures only  if you have the tools to make the stuff there is not in my mind a huge need to get that complicated :)




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"You have brains in your head. You have feet in your shoes. You can steer yourself in any direction you choose. You're on your own, and you know what you know. And you are the guy who'll decide where to go."
                                                                                                                                                                                                                                                                                     Dr. Seuss

Here's  the link. Thanks for reminding me it was a terrain prop. I couldn't find it before. ;) https://forum.reallusion.com/PrintTopic273870.aspx

On related note to an earlier post, the heightmap terrain cannot use Substance materials, or displacement (it's not available for heightmap terrain).

hehe thanks rampa sorry I post and run.   I should slow down ^^.

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"You have brains in your head. You have feet in your shoes. You can steer yourself in any direction you choose. You're on your own, and you know what you know. And you are the guy who'll decide where to go."
                                                                                                                                                                                                                                                                                     Dr. Seuss