Here’s how to make a quick cliff assuming you have piece of cork bark or similar. I think the same would work with driftwood (I have seen suitable pieces at the local aquatics shop).
Take the bark and anchor it down – I glued a piece of thin plywood to the base to make it stand in place for fitting into a railway layout (you can see it in context here).
Then paint the bark in a matt grey emulsion or similar and give it a drybrush highlight with a mix of white and grey then a final touch of white only to give more of a craggy 3D appearance. A nice quick job this one.
You can use pva glue to glue on static grass, clump foliage or the like at likley places on your new “cliff face”.
The cliff can then be places into your scenic hill, mouintain, side of waterfall etc.
Imagination is the only limit (name that sci-fi tv series the quote came from!)
I added three metal HO scale figures in climbing poses and connected them with a piece of thread. The figures come with pins moulded into the feet or belly so you can make a small hole in the layout and glue them in easily.
If you want to see the whole railway project with the cliff in full context, click here.