Symbolism, Imagery, Allegory
If Moon Shadow were Charlie Bucket, the Land of the Golden Mountain would be his chocolate factory. In other words, Moon Shadow has major hopes for America, and who can blame him? He's been told all kinds of fantastical things about America, like you can just scoop gold off the ground in buckets (1.16). But Moon Shadow mostly cares the Land of the Golden Mountain because that's where his dad is. When he arrives in America, he soon sees that the Land of the Golden Mountain isn't all that it's cracked up to be; but his dad is cool. He realizes that what he imagined America to be can be found in America; that is, the awesomeness that he was expecting the Golden Mountain to be can be found in the friends he's made:
I had found my mountain of gold, after all, and it had not been nuggets but people who had made it up: people like the Company and the Whitlaws. I had not realized until I had left it that I had been on the mountain of gold all that time. (11.46)