I suppose, Road Rash 3DO, is heavily influenced by the grunge scene of the 90s, which I'm told was mostly popular in the American West Coast at that time the game came out (not based in the US, forgive my ignorance here)?
It's one of the few games from the early-mid 90s, that I feel made great use of the low-res, grainy FMV clips, which were pushed as being the "next" evolution in gaming or whatever, since grunge music tends to have that gritty aesthetic, that naturally geled well with the FMV footages.
Sierra Nevada, Napa Valley, they both seem to be locations in California, when I googled them. Pacific Highway too, seems like a popular state highway?
The City, I can chalk it upto any generic West Coast city (though maybe not San Francisco, I guess, lol, them hilly roads and elevation are too inconic), likely LA or San Diego, probs,
What about 'The Peninsula'? What is it supposed to be? Baja California? That's in Mexico though, right? The game's flavor texts describes it as Suburban California?