@Marcski, one of these years I want to get to Royal Gorge too. The race organizers had to change venues due to unusually warm conditions, and they spread the races around. Let's see if I can get this straight:
The 50km and 30 km races were indeed at Royal Gorge.
Prologue, sprint and 15k/10k - all at the Auburn Ski Club at Donner Summit.
Hillclimb: Sugar Bowl Resort.
Check out Far West Nordic's YouTube channel, they have separate videos of all the races. The 50 km looks particularly brutal: icy fast early, then sloppy and way slow as it warms up.