If significance of architecture since 1960 is what John B. is asking here I would pick Sand Hills, and Pacific Dunes and others such as Friar's Head, Rustic Canyon etc.
Why? Because in my opinion, those courses are not just an important turning point in the overall evolution of architecture in America but the direction in which they turned is incredibly interesting!
America is the great innovator and American courses and American architects, even if around the world, did a ton of architectural innovating in the last fifty or so years. They used far more innovation through modern technologies than any others, it would seem, to create massive and impressive creations out of blank canvases or natural canvases that weren't used as they were---certainly courses like Shadow Creek are the best examples of that.
But courses like Sand Hills, Friars, Pac Dunes, even Rustic, seem to demark the point where architecture decided to go in the opposite direction finally. The latter courses are obviously at the very end of a 40-50 year cycle in style and type and the latter courses are a bringing in of an entirely new style and type---but one that happens to be a reversion back---a renaissance, in fact, to much of what was long ago---to find interesting to really interesting natural sites and just going with them pretty much as they were as an architectural expression.
It wasn't just that those latter courses were a turning point--the direction in which their type and style turned (back to a former time) is what's most interesting and consequently most significant, in my opinion.
The even more interesting thing to contemplate is that this new renaissance type and style really is a significant point in the evolution of it all---it is a new wave and it will hit a critical mass soon if it hasn't already and plenty of it will be produced. But eventually it too, in perhaps 40-50 years, will have run its course, will have run out it's cycle!
And then, where will the art and the evolution of architecture go next?