The station holds the oldest active radio license in the Yuma market, first signing on March 3, 1940 as KYUM at 1210 kilocycles on the AM dial. It was a NBC affiliate and operated with 250 watts during the day and 100 watts at night. KYUM moved to 1240 AM on March 29, 1941, then to 560 AM with 1000 watts full-time on March 29, 1951. By the late 1960s, the station had come under the ownership of Combined Communications.
Radio station KBLU signed on September 6, 1959 as a 500 watt, daytime-only station at 1320 AM. It was founded by Robert Crites, and, with its television sister station, KBLU-TV (now KSWT), became part of Eller Telecasting in the late 1960s. The station had a top 40 music format and was affiliated with NBC radio in the 1970s.
In 1969, Eller Telecasting sought to merge with Combined Communications. The FCC approved the merger on October 22, 1969, but required that Combined Communications divest itself of either KBLU or KYUM. Due to a stronger signal and favorable dial position, the parent company chose to keep the 560 AM license and to donate the 1320 AM license to Arizona Western College so that it could start its own radio station, KAWC. The KBLU call sign and intellectual unit transferred to 560 AM.