With the ice caps gone and Greenland vanished, the oceans buried every city on the coasts. Potter's hometown of Spotsylvania was under water, and the Shenandoah valley was a shallow sea because there was no drainage, with the Atlantic lapping at the eastern base of the Blue Ridge. Houston was gone, and the skyscrapers of Dallas-Fort Worth were empty shells on a lifeless beach.
Oklahoma City was a village, its "river walk" filled with sand, its rivers dry, its energy companies vanished. The last earthquake had been more than a 9 on some forgotten scale, and collapsed the city's newest building, an energy company skyscraper. Potter thought it ironic that Tulsa fared no better, its statue of a senator who once called climate change a hoax presiding over vacant, dusty streets and empty oil storage tanks.
Most of the survivors of the famine and disease were like Potter, living in mountains like the Cascades and Alaska and Rockies and Ozarks and Appalachians and Poconos where they could still get groundwater and altitudes cut the heat. That's where what remained of governments existed, where power was measured in the amount of water controlled.