As tastes and technology began to change, the old bastions of youth culture started to slowly fade. Pop Culture and rock n' roll were synonymous with AM radio ever since the early 1950's. The reason was rather simple - Radio was undergoing a huge change in its audience, as TV crept into every home in America and was becoming abandoned as the primary source of entertainment. Much of what had been popular on radio since the 1930's simply transformed itself to television, leaving Radio stranded and looking for an audience as well as ad revenue. When Rock n' Roll came to light, it found a tailor made goldmine with AM radio because a: most adults were too busy with TV to notice and b: every American car had an AM radio. It was perfect and it stayed perfect for the better part of two decades.
And then music changed. Albums were replacing singles and longer cuts became impractical for formats structured around the two minute cut. Coupled with the spreading popularity of FM which, up until 1968 was broadcasting primarily for the high-end Audiofile crowd or simulcasting the AM counterparts of stations who owned both AM and FM stations, and the auto industry who were now installing FM radios as standard equipment, the writing was on the wall for AM radio as a center of Youth Culture.
In 1968 one of the most popular rock radio stations in Los Angeles, KFWB, was sold and the new owner was eager to dump the music format in exchange for all news (a new concept at the time). So on March 11th, KFWB played their last batch of 45's and bid a teary-eyed farewell to one part of music history before the next one popped up weeks later; FM Underground.
Here are the last 40 minutes of that broadcast as it happened on the evening of March 11, 1968.
Always evolving. Strangely, KFWB just dropped their all-News format in favor of another format; talk-radio.