Plagued by migraines and seemingly allergic to the sun-dappled environs in which she spent so many of her years, Joan Didion nonetheless wrote into being a host of characters that participated in a dissolute Golden State fantasy. Her stories from the 1960s evoke the siren cupidity of a nostalgic, decidedly prelapsarian California, even as they admit an illusion fraying at the seams. That her essays from the other side of the long decade comprise such...