The 50s had Rock 'n Roll (Elvis etc.).
The 60s had the Rock sound of the Beatles with some folk music coming on-line at the end of the decade.
The 70s had the folksy rock mixed with protest music from Vietnam, more guitar in the rock, Southern Rock and Disco at the end of the decade.
The 80s had hair bands and new wave
The 90s had Grunge and things like U2, Red Hot Chili Peppers and Pearl Jam.
Every decade has pop and country. I suppose country has evolved away from twang, but I don't follow country enough to really categorize its eras.
One of my kids was asking what I thought the enduring music sound of today would be. I had no answer. There is some good alternative stuff, but it doesn't really seem like its own sound to me.
Thoughts?