If you have ever seen the old (1999) movie Blast from the Past, you probably remember the ingenious premise. A suburban American couple in 1962 decides that an atomic war is about to begin. The husband has prepared a secret bomb shelter underneath the house for just such an occasion and he leads his pregnant wife there. For 35 years the family remains hidden and when their son finally emerges, he discovers the world has completely changed. No atomic war came, but their neighborhood has turned into a slum and the people he meets are unfriendly and greedy. In the movie this encounter leads to romance and comedy, but what would going back to an old neighborhood after 35 years really be like?

Reading David Talbot’s Season of the Witch (2012) has reminded me of how dramatically and quickly American cities can change. Talbot’s book is a well-documented history of San Francisco from the 1960s until the 1990s. During that time the population of the city did not change much—hovering in the 700,000 range—but the people and the mood of the city altered sharply. New groups arrived in the city and many descendants of earlier residents drifted away.

Talbot begins his book with 1967, the Summer of Love, when San Francisco attracted crowds of young people demanding peace, love and an end to war in Vietnam. The staid citizens of the city, many of whom looked back on World War II as the proudest moment in American history could not understand why young men were unwilling to become warriors. Conflict was inevitable, but the hippies learned to provide their own services to take care of the young people flooding into the city. Eventually the war ended, the runaways went back home or settled down in the city, but San Francisco was never the same. Many memories of the city of love are still alive in the minds of city residents.

No city can remain a city of love forever and the days of love and trust faded away as drugs came into the city and with them some brutal crime sprees that shocked residents and titillated the rest of the country. The zodiac murders were especially brutal. And later came the trauma of Jonestown when hundreds of people—men, women, and children—died under the guidance of a charismatic but deluded minister. Drugs, death and destruction all became part of the indelible history of the city.

Reading Season of the Witch makes you aware of how swiftly and irrevocably a city changed over a short period of time. The gay community gradually overcame the fear and resistance of many of the city’s more traditional residents. Today the city is a center of LGBTQ life. The Gay Pride parade became an emblem of the city and the movement it started spread across the country and around the world. The tragic crisis of the AIDS epidemic might have torn the city apart, but instead it seemed to bring the city together in working to heal the sick and find a cure.

All of this happened within the lifespan of one generation. Each decade brought the city another influx of people with new ideas and ambitions. And now a new wave of people have come, bringing another source of tension.  Well after the period covered by Talbot’s book, came the invasion of the “techies”, welcomed by some and hated by others, but undoubtedly a group that must be reckoned with.

The prices of houses, condos and rentals have soared, streets have become crowded with cars, bicycles, and scooters and giant buses have appeared to carry the newcomers back and forth to their jobs in Silicon Valley and elsewhere. And now developers are hoping to push height limitations on new buildings to accommodate the newcomers. Will San Francisco eventually become a city of high rises like so many other cities around the world? That remains to be seen, but one thing seems certain—it will not remain the same.

Centuries ago Heraclitus told us “There is nothing permanent but change” and it is still true.