From Nookipedia, the Animal Crossing wiki
Mountain Song is a song that K.K. Slider sings. The mountains referred to by the title might be, judging by the yodeling, the Alps. At first it is very contained with an accordion. Then, there is a yodeling effect created by a synthesizer. The accordion plays through the whole song. Beau and Norma play this song if they have a stereo in their homes. Caroline, Del, and Margie are on the boxart.