Day of Wrath (1985)

An American TV-journalist is interested in the trail of some strange mystery embedded in a mountainous region of the USA. After much red tape, he is allowed to enter the area. A sullen guide convoys him through several farms inhabited by even more sullen and withdrawn people. The journalist cannot help minding their weird behaviour, and especially that of one kid who also seems to be a math whiz. With some effort, he discovers an explanation to the mystery and convinces his guide to help him reveal it to the rest of the world.