My backdrops are 1/8" styrene from a local plastics supplier (Tap Plastics). I get the sheet cut into 1 foot by eight foot strips, then glue it onto supports at the back of each scene. After priming and some sky blue paint (fading as it drops to the horizon), I've got an acceptable scene.
The big message here, of course, is that the backdrop doesn't have to be very good. These photos are close-ups and aren't great when examined in detail, but when the whole scene's looked at, they're not the center of attention. They just register as sky colors and hill colors, and that's enough to convince the viewer that the scene is real. Backdrops are also really forgiving; if the painting doesn't work out (as the Glenwood scene didn't at first), just paint a new set of hills on top of your not-quite-good version.
Google Earth's normally viewed top-down, but it also has contour maps so it knows the height of features. If you tilt a Google Earth scene (check the on-line Help to see how) , you can look at an edge-on view of nearby hills. In my case, I found spots along the west side of Los Gatos Canyon, and looked towards the east side of the canyon with the view tilted almost horizontally. I then did screen captures of the scenes, printed them on photographic paper in my cheap ink-jet printer. I then sprayed the images with Testor's Dullcoat to cut glare on the image, cut out the sky portion of each image, and glued them to the backdrop. The first picture shows one of the more realistic parts of the backdrop. The second (over the water tank) worked less well, but is still quite presentable. The only problem with the images is that they're captured from aerial photos, so trees and hills often look a bit stretched and flattened when I tilted the image to look at it sideways.
That last picture also gives away the source of the photo. If you look at the larger version of the image, you'll see a small, bright green line at the top of the ridge. That's Google Earth's way of displaying roads, and I'd forgotten to turn off road displays when capturing the image.