The Long Tomorrow

No city, no town, no community of more than one thousand people or two hundred buildings to the square mile, shall be built or permitted to exist anywhere in the United States of America. --Constitution of the United States, Thirtieth Amendment
Two generations after the Destruction, rumors persist about a secret desert hideaway where scientists worked with dangerous machines and where men plot to revive the cities. Almost a continent away, Len Coulter has heard whisperings that fired his imagination. And then one day he finds a strange wooden box...
The Long Tomorrow is on several major what you should read lists, including the NESFA Core Reading List and Gardner Dozois's Recommended Reading List as well as the Best 105 SF Books Since the Invention of the Field in the Twenties As Compiled by David G. Hartwell and Science Fiction: The Top 100 Novels, by David Pringle, a list compiled in 1985.