KJAC is a commercial radio station located in Timnath, Colorado, broadcasting to the Fort Collins-Denver, Colorado area on 105.5 FM. The station previously aired an adult hits music format branded as "Jack FM".
Jack FM Denver was the first Jack radio station in the United States. Denver's Jack employed a comedic irreverence in its presentation, and a style of music endemic to the varied tastes of Colorado's front-range listeners. Each Jack station is a little different, and KJAC's attention to the style of Colorado gave the station a unique and local feel. Source