Valleysman only had one god an' her name it was Sonmi. [...] Down in Hilo they prayed to Sonmi if they'd the moddin' but they'd got other gods too, shark gods, volcano gods, corn gods, sneeze gods, hairy-wart gods, oh, you name it, the Hilo's birth a god for it. The Kona'd got a hole tribe o'war gods an' horse gods'n'all. (6.1.28)
The Big I is like a little microcosm of the entire world. There are single-deity faiths, and there are faiths with entire pantheons of gods, even though all of these people live on the same island.