We used Foamies—from the local craft store—for all roads. They're even the right colors for asphalt and cement and the right thickness as well (1/8").
For mountains we created profile boards of ¼" plywood and screwed them securely to the layout, then added newspaper and masking tape to flesh out the mountains. We used paper towels and Hydrocal to form a base. After two days drying time, we added plaster and plastered in some rock castings. When the plaster was only partly dry, I used a stiff wire brush and added horizontal texture to some of the rock faces. We colored the mountains with the standard methods of ink/water sprays, acrylic paints, Woodland Scenics pigment solution spraying, then sprayed Scenic Cement and added various turf, dust, vines, talus, shrubs and trees. (The latter required drilling holes and gluing the base of the tree trunks with Elmer's glue.)
A trestle bridge (14) and two girder bridges (1 and 16) were installed in addition to the double-track arch bridge (13 and 12) mentioned above. The double girder bridge was created by cutting a single girder bridge in half lengthwise and gluing a rectangle of styrene plastic to the two halves to form a wider bridge. We then CA-glued timber "planks" on top and stained them with wood stain gel. (Figure: 1 square = 1 inch.)
We transformed a great DPM kit, "Gripps Manufacturing" (9), into "Abracadata Computer Designed Furniture" with a mere sign change. Walthers' "Water Street Terminal" (7, 8 and 3) became "AbraVille Freight Terminal." And Bachmann's rural freight station (4 and 5) became "AbraVille Station." To these buildings we added a gas station (10), house (11), passenger platform (6), a roadside shanty (15), cars and trucks, a park scene and many street and RR signs. We used Woodland Scenics light gray, fine, #B74 ballast. For walls we used a few plaster retaining walls and several paper brick walls from Faller.