Another city would be picked to represent the rest of California, and the point is that using that city as a time zone ID would then work not only for future ti

Another city would be picked to represent the rest of California, and the point is that using that city as a time zone ID would then work not only for future times, but also backwards for any times in the past. If, instead, you had America/California, or US/Pacific, those would be ambiguous either forward or backwards in time. So the trade-off is timezones being specific to a particular city but remaining unambiguous forward and backward in time. You can’t avoid pain when there is a change in the geographic area of a legislative time zone. But you can avoid the case of a time zone ID becoming ambiguous in terms of the UTC<—>local time mapping it’s supposed to define. The latter is the aim of the present scheme.