Wade Hampton is traditionally considered the Best Mountain Course in North America and it is indeed a fine example of integrating golf into an elevated, mountainous terrain. It fits nicely and plays very well. Banff Springs, Pikewood National, Lookout Mountain, Red Sky, and quite a few others usually enter the conversation as well.
With respect to all the above, I find myself seconding Jim Nugent with Stone Eagle.
It's undeniably built on and into the shoulders of the San Jacinto and Santa Rose mountains and aesthetically blends better than those previously mentioned courses. Instead of conventionally moving up and down the valleys and occasionally crossing a few, this iconoclastic design that works on every level. It moves up, down, across, and alongside the mountainside elevations and slopes using the land brilliantly to add interest and playability. It feels seamless as opposed to corridored.
Interestingly, it gets less attention and fame than Tom's other, more regaled work. I've always felt that when compared straight up with other mountain courses, Stone Eagle shines and deserves far more respect.
PS....Tim, despite being close to mountainous terrain, neither Glen Falls or Ekwanok are really mountain courses. Neither has the kind of elevation previously discussed integrated into their routings.