Corruption is a theme that can be seen from multiple angles in Green Grass, Running Water. Corrupted myths play a large role in this story, from the American westerns that Lionel peddles at his job to the myths that the author intentionally corrupts in order to try and restore some justice.
The book opens with what some might call a "corrupted" version of the Judeo-Christian God, in which God is framed as one of Coyote's dreams gone astray. In this version of the story, it is not Coyote who is the corruption, but the Judeo-Christian god. King layers narratives and weaves them together, in one sense "corrupting" them but in another sense creating something new.
This is one of the issues of identity that the book raises: to what extent is something a disruption, a corruption, or an act of creation? Yes, King is changing American myths, but he is also placing his Native characters in the hero roles that Western society has long denied them. It is an act of disruption that aims to rectify the corruption of indigenous American cultures by Western settlers, or in other words, an act of restoration.
Other corruptions abound: Portland's fake nose is a corruption of his real self, created in order to meet white peoples' ideas of what a Native American should look like. The destruction of Eli's cabin in the flood can be considered corruption, but in this case, one that might have been necessary for change.