Complex sentence: In 1912, Fathers Cantwell and Michael D. Connolly accompanied Bishop Edward J. Hanna from Rochester, New York to San Francisco where after Riordan's death in 1914, Cantwell served as Vicar General to Archbishop Hanna (1915--1917).
Split into simpler sentences: In 1912, Fathers Cantwell and Michael D. Connolly accompanied Bishop Edward J. Hanna from Rochester, New York to San Francisco. After Riordan's death in 1914, Vicar General Cantwell served San Francisco Archbishop Hanna (1915--1917).