Although Victor Kilian, as Dr. Morley, is clearly the star of the film, he received no screen credit because he was blacklisted shortly after completing the movie, a victim of the McCarthy "Red Scare" hysteria sweeping the country at the time. This was perhaps the only instance in Hollywood history where the leading actor in a film was deliberately not listed in its cast while everyone else was.
Both the mountains mentioned, Mt Lefat and Mt Neleh, are fictional.
There seems to be some inspiration for this film taken from Jules Verne's "Journey to the Centre of the Earth". Both feature an underground sea. In both, the entrance to the Earth is close to the top of the Earth (Iceland in Verne's novel and Alaska in this film) and the escape from the underground is unexpected and amazingly rapid.
This project was actually put together by two special effects men, Jack Rabin and Irving Block, who are listed as producers.