To Avanti,
I would very much appreciate if you could provide more detailed ‘how to’ techniques for making those realistic sedimentary rock facings. Your recommended model making guidelines for making it look so natural.
Walt,
I'll give it a shot:
It is really pretty simple, but there are a few tricks.
1) First and most important, break the tiles, don't cut them. Just snap each one apart and stack them. They will look pretty good right out of the gate. Glue them together with hot glue. Don't be too neat or regular in the stacking.
2) Study real stone formations as you drive down the highway. Looking at other modelers' work is all well and good, but getting a good feel for what blasted and natural rock faces really look like is better. In particular, look at all the imperfections -- gaps and unevenness in the beds, places where vegetation has gotten hold, variations in rock color and thickness, etc.
3) Keep in mind that even though all bedding planes were originally formed horizontally, you will rarely find them horizontal today. Over the eons, they have been squeezed, shifted, and folded every which way.
4) Don't be afraid to add a fault or two--places where a crack formed perpendicular to the bedding planes--possibly with a different pitch on each side of the crack.
5) Start by spraying an uneven coat of flat black paint. Trust me on this one. Just as you should end by dry-brushing with a bright white to simulate the glint of sunlight, you should start with a stark black to simulate the deep shadows that form in nooks and crannies on a sunny day.
6) Next, spray on your basic rock color with a very flat spray paint, most likely gray or light brown (or both). "Camo" spray paint colors are a good choice. As always, don't be too even or uniform. Cover the black, but not too well. Spray at an angle, so the crannies retain some visible 'shadows'.
7) Brush on some light patches of green and dark brown here and there. Cheap craft tempera paint is fine for this. End with the normal dry-brushed white.
8) Let the paint dry, spray on some dilute white glue, and sprinkle (or blow) on a mixture of sand, small gravel or kitty litter and something brown (dry coffee grounds are good). You are trying to simulate earth, rocks, and scree. Make sure that most of the material lands on the horizontal surfaces and in cracks that would naturally accumulate such stuff. Don't overdo it and don't be uniform. Nature is never uniform.
9) Add various sizes and colors of ground foam, bits of lichen from the bottom of the bag, and some stretched out flocking to simulate vines.
10) Maybe add a few struggling little trees or scrawny bushes here and there.
11) If its seems necessary, finish with another coat of dilute white glue to hold everything together.
12) Be sloppy and have fun.
What a great idea!! 
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