KEEN also featured live sports coverage; it broadcast the San Jose State Spartans and Santa Clara Broncos in the late 1950s and throughout the 1960s and the Oakland Athletics during the early to mid-1970s.

In 1993, KEEN went silent for several months after losing its transmitter license and returned to the air in 1994 as KKSJ and a pop standards format branded "Magic 1370."

Founded by United Broadcasting Company, whose president was George Mardikian, KZSF came on the air in 1947 as a 1,000 watt station with call sign KEEN and a transmitter on a North San Jose orchard near the town border with Milpitas.

[4][5] At 8 p.m. on June 21, 1947, KEEN's grand opening broadcast took place at the Hotel De Anza in Downtown San Jose and featured comedian Red Skelton.

[6] Programming included news from the United Press,[3] Saturday night barn dances,[7] and University of Santa Clara baseball games.

[21] After over 25 years operating out of Hotel De Anza, United Broadcasting moved the KEEN and KBAY to West San Jose in 1974, on the top floor of the Golden Pacific Building at Winchester Boulevard.

[24][25] These factors led United Broadcasting to announce that KEEN would be a simulcast of easy listening FM sister station KBAY.

[26] However, beginning April 1 that year, KEEN cut its on-air staff to three hosts during daytime hours and broadcast syndicated music by satellite in other time slots.

[27] KEEN went off the air on January 1, 1993, after losing its transmitter lease a month earlier as the city of San Jose planned to build nearly 250 houses in the area.

[5][25] After United Broadcasting made an arrangement for KKSJ to share the transmitter site near U.S. Highway 101, a Union Pacific Railroad overpass, and an Eggo factory with fellow San Jose AM station KSJX, KKSJ resumed broadcasting in 1994 with the brand "Magic 1370" and a pop standards format inspired by the former "Magic 61" brand of San Francisco's KFRC.

[33] American Radio sold KKSJ to Douglas Broadcasting for $3.2 million in June 1997 and changed it to an Asian ethnic format with Vietnamese and Cantonese programming.

[58][59] On weekdays, KZSF broadcasts a variety of Mexican music, including a nightly program dedicated to corridos and ranchera, along with Spanish-language public affairs, advice, and sports talk shows.

[60] Celina Rodriguez, a former news anchor for local TV stations KDTV and KSTS, has hosted a talk show on KZSF since 2006.