This is near Salt Lake City - I believe slightly SE.
Homestead Crater | Midway Hot Springs | The Cater Utah
Since it's geothermal - they've introduced some tropical fish. I believe there is/was a resident shark also.
I'm not sure I believe this since last time I checked, Florida was a state but:
THE CRATER IS THE ONLY WARM SCUBA DIVING DESTINATION IN THE CONTINENTAL US.
From there cut across the state and dive the shark tank at Mandalay Bay casino in Las Vegas.
Possibly dive the B29 in Lake Mead - depending on how full the lake is now, it's either a deep rec. dive or a tec dive. There's a couple outfits with permits to dive it - Tech Diving Ltd. in Havasu is one of them.
I'd pass on Lake Powell, there may be one dive shop left there but it's a kayak place that does some diving.
I've also seen people diving in Lake Tahoe but have no details. I don't believe there's a shop there either.
Then take I-5 to the Pacific and work your way up the coast - especially diving the Kelp Sanctuary in Monterey - not to be missed.The only areas that diving is marginal is around SF Bay.
There's some good diving around LA also - boat diving in the Northern Channel Islands from the Ventura area - or farther south in Long Beach - there's a fleet of dive boats diving the coast and Catalina Island. You can even take the Catalina Express over to Catalina - so many divers do it, they're set up to handle dive gear. I know people in LA who dive the Marine Park there and back in the same day - an overnight would be easier. I believe the Express has secured parking for your stuff but check.
From the Monterey area, LA is a full days drive south. And you have consider traffic patterns in the LA area - not just driving distance.
Bring the heavy wetsuit or drysuit if you've got one.
I don't think there's much diving in the Dakota's, Idaho, Montana, Wyoming or Nebraska.
sounds like fun.
