Complex sentence: Baum had been active in the group since he first moved to Los Angeles in 1909; he served among the Excelsiors, the group's governing board, he wrote and acted in their shows, and he played the bass drum in their band.
Split into simpler sentences: Baum had been active in the group since he first moved to Los Angeles in 1909 and served among the Excelsiors, the group's governing board. He also wrote and acted in their shows and he played the bass drum in their band.