Story of a Song is a monthly segment on KCUR's Central Standard , in which local musicians tell the story behind a song they have written or are performing. The band: Jorge Arana Trio The songs: "Mammoth," "Speak Beast" The story: "It started with a very simple riff," says Jorge Arana, of his latest album "Mammoth." It reminded him of something out of an old Western . At practice, the band played the riff, over and over again, letting it build in intensity, but keeping those same, simple notes.