The novel is set in California in the 1960s with Oedipa yo-yoing back and forth between the San Francisco Bay Area and Los Angeles. Pynchon lived in California for several years in the 1960s, and though he initially flirted with the radical culture there, it seems that he later turned away from it. The Crying of Lot 49 gives him the opportunity to parody the culture in which he became immersed, however briefly.
Although Lot 49 is an experimental book that plays with narrative form and the nature of fiction, it is also totally spot on as far as social detail goes. At one point, Oedipa walks across the campus of the University of California, Berkeley:
She came downslope from Wheeler Hall, through Sather Gate into a plaza teeming with corduroy, denim, bare legs, blonde hair, hornrims, bicycle spokes in the sun, bookbags, swaying card tables, long paper petitions dangled to earth, posters for undecipherable FSM's, YAF's, VDC's, suds in the fountain, students in nose-to-nose dialogue. (5.10)
The description goes on and on. One senses that Pynchon could catalog the details of Berkeley's social life endlessly. Throughout the book, there are references to the John Birch Society, to the March on Washington, to Senator Joe McCarthy and the Red Scare. In some ways, Lot 49 is an unlikely book to serve as a period piece of 1960s California (since it's a surrealist comedy with a plot that goes all the way back to Europe in the sixteenth century), but Pynchon gives a very detailed sense of the time.
Today, things have come full circle and the book itself is considered an iconic artifact of 1960s counter-culture. In other words, you're not just holding a book that depicts California in the 1960s, you are holding a piece of California in the 1960s.