The hardiness zones are based on statistical averages so it will depend on what set of data is being used by the USDA, for example, or anyone else. I'm not sure what GW is using. I just use USDA because it's the most widely used by other things I use like weather apps, planting schedules, etc.

Pagan

Agree with the above. Also within each zone are micro-climates, so you really almost have to take the USDA and modify it for what you actually know will and will not grow on your land. I use the interactive map so within my region I can see the various microclimates. There are 3 colors within a 20 minute drive from me. I know very well that it does freeze in the valley below because I hear the loud commercial citrus growers turbines go on in freezing conditions, where up here, it just doesn't freeze. We can grow avocados, mangos, etc. here, but down the hill, they can't.

So I will just call me a micro-climate. It does very. Especially with this drought. I also live above a long canyon that goes straight to the Crystalview mnt range.