"There's enough solar and thermal energy in Death Valley alone to power the United States year 'round, I have read somewhere, but for good reason no-one has ever built a HV distribution backbone into the area. So it would be costly to get the energy out to the grid."

Ah - the grid was built to go to Niagara - more or less... so if we HAD gone the thermal path, the grid would have gone there... you heard the old tale how winding goat tracks become winding highways?