KMPX (106.9 FM) was a San Francisco FM radio station which was best known in the late 1960s as the birthplace of America's freeform progressive rock format ("Underground radio") and in the 1970s as the only station nationally devoted to playing big band music full-time.
On December 10, 1959, the station, owned by San Francisco businessman Franklin Mieuli, signed on at 106.9 MHz with the KPUP call letters.
In July 1960, the call letters were changed to KHIP and the station aired jazz music programming. Mieuli sold KHIP on July 1, 1962 to Leon Crosby, who had previously owned KHYD in Hayward.
Under Leon Crosby's ownership, the station began operating in multiplex stereo and the call letters were changed to KMPX (for "MultiPleX") the following month. Soon after, Crosby gained authorization by the FCC to increase the station's power from the original 37,000 watts to 80,000 watts. The transmitter was in Marin County on Wolfback Ridge above Sausalito.
By mid-1964, KMPX was airing a middle of the road music format. As the money-strapped station struggled, by 1966 the schedule became dominated by various foreign language and other brokered programs.
Though KMPX's daytime schedule was heavy with ethnic programming, the midnight-6 AM slot was mostly open. On February 12, 1967, on-air personality Larry Miller was given the shift, where he played his preferred folk rock music whenever a foreign language show was not scheduled. But even with this impediment and the station's high-end-of-the-dial position, word spread that "rock and roll is on FM".
A month later, Tom Donahue, a former well-known local Top 40 disc jockey on KYA, fledgling record label owner and concert promoter, was looking for an opportunity to do something unique on the radio. According to his then-girlfriend (and future wife) Raechel's recollection, mentioned in Jim Ladd's book Radio Waves, after spending a night listening to The Doors' first album at home, Donahue wondered why radio stations weren't playing it. He soon started calling around town to local stations on the less-desirable FM dial. When he found that KMPX's phone was disconnected, he decided to approach Crosby with his plan, as he felt the station had nothing to lose. Donahue proposed to take over some of KMPX's programming and replace the brokered foreign-language shows with freeform album-based rock music, declaring, "no jingles, no talkovers, no time and temp, no pop singles." Advertisers would come in the form of local businesses serving the local hippie and Haight-Ashbury communities. As Donahue was a well-known and respected person in local radio, Crosby hired him.