Yeah, and I suppose there are many different canyon-like spaces they could be in. But the more this goes through my head the more certain I am that it's in the Sunnydale crater.
SF to Santa Barbara County is about 5 hours driving, which fits well enough in the timeline. (Santa Barbara county is widely believed to be where Sunnydale would be, from wikipedia for ease: The episode Pangs reveals that Sunnydale is in the former homeland of the Chumash people, which is the area northwest of Los Angeles, centered on Santa Barbara County." Further supporting this, in Shadow "805" is established as the area code for Sunnydale, and one of the three places it might be is Santa Barbara County--either way, we're working with somewhere close to the ocean and the desert with an international airport and one Starbucks).
Further, I feel like Buffy's expression upon seeing it was peppered with annoyance, and seeing her Sunnydale crater being used thusly would certainly do that (let's hope that hell mouth is really quashed, eh?).
Also, when half your prisoners are vampires it seems other-worldy cruel to make them all live somewhere that is incredibly sunny. Take them to Washington!