Surfer boys & girls, Lorne, 1975 © Rennie Ellis Photographic Archive
TuskedBeast contributed the insightful theory that "summer music" is more of a shared experience than a calendar phenomena.
So very true and obvious once someone points it out.
I did some searching with the way-back machine and came up some Billboard hits for the time period in question.
1. Love Will Keep Us Together, The Captain and Tennille
2. Rhinestone Cowboy, Glen Campbell
3. Philadelphia Freedom, Elton John
4. Before the Next Teardrop Falls, Freddy Fender
5. My Eyes Adored You, Frankie Valli
6. Shining Star, Wind and Fire
7. Fame, David Bowie
8. Laughter In the Rain, Neil Sedaka
9. One of These Nights, Eagles
10. Thank God I'm a Country Boy, John Denver
11. Jive Talkin', The Bee Gees
12. The Best of My Love, The Eagles
13. Lovin' You, Minnie Riperton
14. Kung Fu Fighting, Carl Douglas
15. Black Water, The Doobie Brothers
16. The Ballroom Blitz, Sweet
17. (Hey Won't You Play) Another Somebody Done Somebody Wrong Song, B.J. Thomas
18. He Don't Love You (Like I Love You), Tony Orlando and Dawn
19. At Seventeen, Janis Ian
20. Pick Up the Pieces, The Average White Band
21. The Hustle, Van McCoy and The Soul City Symphony
22. Lady Marmalade, Labelle
23. Why Can't We Be Friends, War
I think this is firm support for the "shared experience" theory because no one would pick this lot out on their own.
Although I have to admit I have always been a big fan of Kung Fu Fighting