Which of these women was married to Johnny Cash?

Everyone knows about June Carter Cash. But Johnny's first wife is not that famous, even though the story of their love was quite beautiful.

Before June Carter Cash, Johnny Cash was married to another woman, Vivian Liberto Cash. Johnny and Vivian were married from 1954 to 1968 and had 4 children, all girls. During their courtship, the lovers wrote each other over 10,000 pages of letters, forming the basis of Vivian's autobiography, titled I Walked the Line: My Life with Johnny, which was published in 2007.