KBAY (at 100.3 on the FM dial) was first granted a construction permit by the Federal Communications Commission in 1959, with the call letters KEEN-FM. Owners United Broadcasting had put San Jose sister station KEEN on the air in 1947.
A series of construction, regulatory and engineering delays meant KEEN-FM didn’t actually begin broadcasting until 1963. One of the hurdles was a protest filed by the Gilliland family, owners of San Jose’s KNTV (Channel 11).
At the time, many Bay Area FM stations with co-owned AM properties were offering a version of what was on the AM station, but KEEN-FM diverged from the AM station’s country music by airing an easy-listening format.
United Broadcasting changed the call letters to KBAY in 1967 (they’d become available when Kaiser Broadcasting switched its San Francisco FM station to KFOG.)
KBAY would stick with various iterations of the soft music format, adding in light pop songs, for the next thirty years.
The big change came in 1996, when United Broadcasting sold KBAY and KKSJ (the former KEEN) to Boston-based American Radio Systems in a $31 million deal. A few months later, American Radio Systems worked out a bigger deal with EXCL Communications. Part of the transaction involved swapping KBAY for KBRG. American Radio Systems moved the KBAY call letters to 94.5 FM and the 100.3 slot became Spanish-language KBRG.