Although Fort Jones is very near to the town, it might as well be on a different planet. It's a place where none of the children go inside except Chonita, and even when she does, she's aware that she's not welcome. During her brief visits to the fort, she becomes acutely aware that there are huge cultural and linguistic differences between herself and the soldiers who live there.
Even though Chonita has learned some of the English words and expressions used by the soldiers at Fort Jones, it doesn't bring her any closer to them. But then, they're not there to fraternize with the locals; they are there to do a job of work: to guard the border and ensure there's no repeat of the troubles a decade earlier.
Technically, then, the soldiers of Fort Jones are there to protect the people of the town. But even so, there's no real connection between the two groups of people. To a large extent, this is because most of the soldiers are white English speakers, whereas the local community consists of Spanish-speakers.
Even though the children of the town learn all about American history at school, it seems that they're still a long way off from becoming fully assimilated into American society. And one could say that Fort Jones represents the cultural and linguistic barriers that separate white from Latino and Spanish speakers from English speakers.