Up to 1,000 or so cell sites went off line due to the extended power shut down in northern California:

Even as California burns, the cell phones of many residents have gone mute, preventing them from giving or getting emergency information.

Source: Kincade Fire: Why you can’t make cell calls in this emergency

Most cell sites are configured with battery backups to keep running during short term outages but are unable to continue running without power for days. Some also have generators but due to the power shut down and wild land fires, they were unable to be serviced with additional fuel.

Some have thought that with communications becoming a commodity, we would no longer need distributed emergency communications from ham radio. Instead, the more communications we’ve built and the more it has been used, the larger the impact of its loss. Amateur Radio emergency communications remains a vitally important component of emergency planning and service delivery.

Coldstreams Skeptic