KNZZ was first licensed on September 16, 1925,[3] as a portable broadcasting station, with the sequentially assigned call letters of KFXJ, to Mountain States Radio Distributors, Inc. in Denver.

[6][7] In 1926, as part of the settlement of Horn's estate, KFXJ's license and equipment were transferred to R. G. "Rex" Howell, a recent high school graduate from Denver and early employee of one of that city's first radio stations, KFEL.

[10][11] KFXJ developed such a strong reputation that it was widely expected to garner the CBS Radio Network affiliation for Denver.

KFXJ signed on from Grand Junction on January 31, 1931, from an Art Deco and block glass building on Hillcrest Manor.

[8] The television station still has the KREX-TV calls, and still operates out of the building Howell originally built for its former radio sister.