The only time I had sushi was in Denver - which, by your opinion is probably worse there than it would be here in Ohio. Next time I'm near an ocean sushi will be one of the first things I'll try.
People keep saying "only eat sushi near the ocean", but that really means nothing for many/most of the items on the menu. Some of the best sushi fish, and some species, come frozen. Quality all depends on how they were originally prepared, frozen and stored.
Hamachi, Octopus, Unagi and many others - frozen, frozen, frozen in most cases. If done properly, it can be better than fresh because there's no chance to decay before serving.
Some things like Mirugai (geoduck) and Uni are pretty much fresh-or-nothing-at-all items, though. I wouldn't eat either in Denver unless the critters arrived live at the restaurant.
And salmon is *always* deep-frozen before serving raw, for safety - salmon is notorious for picking up parasites migrating between saltwater and freshwater; these are killed either by cooking or deep-freezing. You won't necessarily get sick eating fresh raw salmon (sashimi-loving fishermen do it all the time), but the risk goes up substantially. A good chef will take the prime pieces, set them aside for deep-freezing as sashimi later, and grill the rest.