When Was Central Asia Zoroastrian?

The Iranian peoples of Greater Iran are often collectively
characterized as having been "Zoroastrian" in pre-Islamic times. In
order to avoid the pitfalls inherent in such a blanket generalization,
the author proposes that pre-Islamic Central Asian religion be
considered as an ever-changing mix of local and non-local
religious beliefs and practices, drawn largely but not exclusively
from an Iranian pool of myths, deities, symbols and rituals.