I'd need to pore through his book a bit, but didn't George Thomas hate the site at Riviera and offer a ton of backhanded comments on it before starting the work? I theorize that is why it turned out with so many varied, creative architectural solutions--he felt the need to inject some interest into it compared to the more naturally tumbling sites over at LACC and Bel-Air. It's probably also why it is my slight favorite of the 3, despite LA being much better presented and truer to original character.
My first thoughts on this subject were Riviera, Chicago, Garden City, Oakmont, and Seminole. I personally love the setting at Chicago though, and it is definitely not flat, as Tom says. Garden City has the soil going for it. Riviera is actually a sneaky cool site with the original wash-ways and the deceptive tilt of the whole valley. I haven't seen Oakmont or Seminole, but after learning more about it on recent podcasts, it kind of sounds like the "winner." Yes it has the sand ridges, which are cool, but everything else in between sounds like a featureless quagmire of high groundwater and heavier soils. Makes it much more impressive how Ross pulled off that design.