SAN FRANCISCO -- Hippie counter-culture blossomed as the "Summer of Love" unfolded 40 years ago in San Francisco's Golden Gate Park and Haight-Ashbury neighborhood.

Teenagers, college students and other young people flocked to the area, which was a hotbed of psychedelic styles, rock music, free love and drug use. Social change and political unrest - including activism against the Vietnam War and for civil rights - formed a backdrop.

This year, several tours and museum exhibits are marking the 40th anniversary of the Summer of Love, both in San Francisco and elsewhere.

New York's Whitney Museum of American Art is showing "Summer of Love: Art of the Psychedelic Era," now through Sept. 16. The show looks at the impact that the 1960s and early 1970s had on art, music, film and other fields.

The Rock and Roll Hall of Fame in Cleveland has six exhibits that touch on "Summer of Love" themes, including shows about The Doors, the Beach Boys, the "San Francisco City Scene," Otis Redding, Jimi Hendrix and the Monterey Pop music festival, which in 1967 launched Janis Joplin's career and also featured Jimi Hendrix. All of the shows have already opened except for the Beach Boys, opening June 22, and Monterey Pop, opening July 25. Details at http://www.rockhall.com/.

Those who care to retrace the footsteps of the hippies of yesteryear can take San Francisco's "Haight Ashbury Flower Power Walking Tour." The tour is offered Tuesdays and Saturdays at 9:30 a.m. and Fridays at 11 a.m., at $20 a person (children 9 and under free). Details at http://www.haightashburytour.com or 800-979-3370.

Other "Summer of Love" events in San Francisco include a lecture sponsored by the San Francisco History Association at the Mission Dolores School Auditorium, 16th & Church streets, June 26, 7 p.m.; a daylong 40th anniversary concert Sept. 2 at Speedway Meadows in Golden Gate Park, http://2b1records.com/summeroflove40th, and a "Summer of Love Treasure Hunt" sponsored by San Francisco City Guides, Sunday, Sept. 30, 11 a.m.-5:30 p.m. Participants will solve a series of puzzles about people and places from the era, complete with appearances by costumed characters. Assemble your own team of up to six people or be placed in a team the day of the event. Tickets are $35 through July 31, $40 after that and $45 the day of the event. Fees from the treasure hunt will benefit San Francisco City Guides, a project of the local public library that leads free walking tours around the city. Details at http://www.sfcityguides.org/ or 415-557-4266.