Here is an experiment that you can do with friends testing their knowledge about locations. Take a train photograph that includes a mountain range far in the background. Cover the bottom part of the photo that would give away the location. Your friend may still recognizes the location mainly because of the outline of the mountain range against the sky. Think of that outline of a mountain as sort of a geologic fingerprint that we can recognize.
I've included several mountain outlines on my finished Burbank Junction modules, they would be recognizable to folks living in the area. The Verdugo Mountain range above Burbank has several distinguishing features, if you live or have visited the area, they would be recognizable. Same goes for Mt. Hollywood that separates Burbank and Hollywood. Almost everyone recognizes the mountain with its "Hollywood" sign from the Hollywood side, we've seen it countless times in the movies. But those living on the northern, Burbank side would also recognize it from that side.
The point is. . . If your going to model a location, then painting a mountain range should look like the place your modeling.
With reference photos and pencil to draw a line for my mountain range, I use a soft brush to paint a sharp edge of where mountain meets sky. For these distant mountains, I used a color called Wild Ingido, another True-Value brand. Use your photos of backdrop mountains matched to a paint sample card you wish to paint. After painting the sharp edge, I went back with the 1 1/2" brush and filled in below.
Now were going to give the mountains highlights. Over on the finished part of the layout, the mountains are highlighted on the right side, so to appear as the east end of the valley, however because my layout extends to the opposite side of the room, the mountains will be highlighted on the left side for the westward end of the valley.
I used several small, stiff, flat tip artist brushes for highlight the mountains. Have a dish of water handy too. Mix what the brush will pick up of the Silver Sand color and the Wild Ingido on another small dish. Add a little water to the mixture using the highlight brush. Use one brush for the lighter color and the other brush for out of the can Wild Ingido color. Using the highlight color brush, start painting a sharp line on the left or right side of the mountain peak (where the sun hits the mountain), then forming angular shapes towards the base of the mountain. Some angled shapes painted midway down for the foothills. Let this dry, then stand back and take a look. Go back with the full Wild Ingido color and fill the shadow side of the mountains, dry brush some paint where shadows would break tend up the highlight color. Just practice, if you don't like the results, then repaint the Wild Ingido and try again.
The next part of the painting project is really simple, I want to add more haze in front of the mountains and tone them down. Let the paint dry for a day and with the 1 1/2 inch wide brush I added a wash of the Silver Sand color (a lot of water and little paint), that will take it into the sky just above the mountains. Your brush should be only damp, so as not to run, use a rag to remove the excess water, you'll not want to chase runs down the wall. You can also use an airbrush to achieve the same effect.
The painted mountain range that rings the San Fernando Valley on my layout now has that distant look. Time to see how the module frames look set back in place in respect to the backdrop. With practice, this backdrop took less time to do than when I had first started on the finished part of the layout.
A good reference source of pictures for painting Southern California scenery are citrus box labels. It's easy to match the colors for background mountains, sky and trees. I found some useful examples on the Internet. This is part of a citrus label for Northridge Growers in the San Fernando Valley.
Next part of the project will be putting the plywood on the frames and laying track. This will be uploaded to this site as soon as I get finished as the last part of the construction article.