Moon Valley was located on the "dark" side of the moon, making it undetectable by Earth-based observation methods. Moon Valley was 400 miles long, with natural warm springs that created a temperate climate that was comfortable for human beings. Moon Valley was the only area of the Moon that had such springs, as well as vegetation and an atmosphere.
"Days" in Moon Valley were 27 1/3 Earth Days long, divided into 13 2/3 "days" of light and 13 2/3 "days" of darkness. Moon People were long-lived by Earth standards, with the oldest Lunarian on record living to be 1,300 years old.The people of Moon Valley were technologically advanced, and developed the ability to receive television signals from Earth. They used this to research Earth's people and learn the planet's languages. Despite their technological sophistication, the lack of the element titanium on the Moon meant that the residents of Moon Valley were unable to construct their own spacecraft.
Moon Valley's most notable inhabitant was Moon Maid, the daughter of the Moon Governor. Following her death, all interaction between Earth and the Moon was discontinued.
It is unknown if the people of Moon Valley were an off-shoot of the human race that were somehow transplanted to the Moon, or if they are an entirely alien species who settled there. Lunarians' genetic compatibility with humans might tend to suggest the former explanation.
In a 2012 storyline, Moon Valley was shown to have been deserted. The Lunarians' whereabouts are unknown, though the Moon Governor was later shown to be on Earth. The Governor claimed that Moon Valley's oxygen supply had dissipated, but this may have been a ruse.