Just picture it. It would make perfect sense because that location would give them immediate access to Alaska, Canada, Hawaii, Russia, Japan ,and China.
I often wondered where the Enclave has been for the past 200 or so years.
The environment could be this oddly green metal and plastic wasteland, where sickly palm trees grow atop skeletons and mysterious machines that never got out on to the battle field against China.
In the day the sun would generate a warm glow that feeds and strengthens the growing plant life. However the nights are filled with random electrical storms that strikes the metal with thunder powering the mecha-continent's ancient defenses and machinery.
Their would be almost no human mutations and no Super-mutants posing as threats, however as in all Fall-out games, this is a wasteland.
your enemies would most commonly include mutated plant and aquatic animal life or gangsters and raiders. The more ferocious enemies would be rogue computer programs and robots that have the home field advantage.
I would call it the Pacific wasteland, but it's, of course, only a suggestion.