First, the approximately 4"x8" diorama was built with a ceiling tile base, ceiling tile built up for hills as on the layout, a leftover length of Peco flex track, and a cardboard strip for roadbed.  At this point, the hill was shaped, and the "rock face" was carved to blend the different layers together closely (but not exactly).

Then a thin layer of spackling compound was spread on top where ground cover will go.

While the spackling compound was drying, I patched any extreme holes on the rock face, just to blend layers together a little farther (but not too far, as some horizontal fissures are normal for this basic type of rock).  While that was drying, the track was brush-painted with Testor's "rubber", and the edges were painted Rust-o-leum's "Kona Brown", all like the layout.

Then the spackling compound was sanded down, just enough to knock off the peaks and sharp edges, but not near smooth.  Then the track was masked off, and the rock face was painted with an unthinned exterior latex almond-colored paint that was left over from some outside trim work.

Then the rock face was tinted with Woodland Scenics tinting pigments.  Then I mixed a couple of other paints, hoping to get a color brown I was after.  While the paint dried, the grayish brown color turned to a grayish purple, as seen in the picture.  Obviously, the different paints were incompatible, so I had to go and get a paint the desired color.

After a correct color was painted on the surface, and while it was still wet, ground foam was spread out, and secured with diluted glue.  Then, pieces of Woodland Scenics clump foliage was applied to the edge.

Then my scratchbuilt tree was installed, along with fine leaf foliage on the hill, spritzed with hairspray, sprinkled with different colors of fine ground foam for depth, and spritzed with more hairspray.  Lastly, the track was ballasted.

Then the rock face was spritzed with hairspray, and while it was still tacky, I put more fine ground foam on a small piece of paper, and a very small portion lightly "blown" onto the rock face, which gives it a little color, and blends it in with the other scenery.  Another spritz of hairspray was given to hold the foam on.  Then the paint on the track, and other minor details were touched up.