Southern Reach Trilogy

Area X has been cut off from the rest of the continent for decades. Nature has reclaimed the last vestiges of human civilization. The first expedition returned with reports of a pristine, Edenic landscape; all the members of the second expedition committed suicide; the third expedition died in a hail of gunfire as its members turned on one another; the members of the eleventh expedition returned as shadows of their former selves, and within months of their return, all had died of aggressive cancer.