Tropic of Kansas

"The United States of America is no more. Broken into warring territories, its center has become a wasteland DMZ known as "the Tropic of Kansas." Though this gaping geographic hole has no clear boundaries, everyone knows it's out there--that once-bountiful part of the heartland, broken by greed and exploitation, where neglect now breeds unrest. Two travelers appear in this arid American wilderness: Sig, the fugitive orphan of political dissidents, and his foster sister Tania, a government investigator whose search for Sig leads her into her own past--and towards an unexpected future."--

Synopsis from Open Library.