I love structures...industrial, commercial, stations, etc. and they comprise better than 80% of the surface area of my present layout. But, I also love mountains, and unless my hunch is wrong, it seems few model railroaders have mastered mountain building. It is IMO the most challenging aspect of scenery; and as I've perused the last 30 years of O-gauge train magazines, there hasn't been many featured layouts with realistic-looking mountains.
Rich Battista has created superb mountains on his Black Diamond RR - and while I've watched his DVD on how to do them numerous times, I haven't mustered the courage to attempt his method. There's some others as well, including the late John Allen; and, the professional layout builders all have a niche in how they create mountain scenery. A few years ago, and out of desperation, I submitted a scope of work for a mountain valley on my layout to a professional layout builder, a project that entailed about a 9' x 3' two-sided river valley, and the estimate was four times higher than what I was anticipating. I am talking the price of 4-5 Legacy Big-Boys. Needless to say, I endeavored onward myself.
My attempts at mountain building have been less than "great." I use 2" insulation foam covered with structolite or whatever product I can find from Scenic Express or train shows ~ they're kind of like a weak cement - and then use copious amounts and layers of water-based paints and scenery cover. This method is tedious and takes forever to get even something semi-decent looking. The mountain I created on my former layout, shown below, was my best attempt thus far; and I am now incorporating parts of that mountain as well as newly built sections on my current layout. This project took many months and countless hours of frustration as it went from hideous to acceptable. I hope to have something done by this Christmas, though that was my goal a year ago.
In the meantime, if you can share your mountains and secrets please do so...I need inspiration on this front.