In the Mountain's commercials and promo spots, the station is portrayed as nothing less than a transcendent, primitive, spiritual force -- not some tawdry way to deliver customers to advertisers. And while that may be a stretch, as the only commercial rock station to take a sincere interest in music over demographics, the Mountain has done something that non-believers thought impossible: It's kicked ass. Much of the station's success, and its good ratings, can be tagged to afternoon DJ Pete MacKay, who mans the drive-time shift and spins amazingly diverse, music-loving sets that vary wildly from day to day and hour to hour. Like most Mountain DJs, MacKay knows his stuff, from the Fab Four to the Four Tops, Marvin Gaye to Bob Marley, Elvis Presley to Elvis Costello. Witty and urbane, MacKay has an on-air persona that's casual, and his selections are accessible. More adventurous listeners will appreciate his trips to the archives, when he pulls deep album cuts and obscure singles. Tune in and turn on; you won't want to drop out.