Answer: It looks like you're right on the border; in this case I would go with the lower zone number, USDA zone 3. You might want to check out the Sunset Western Garden Book (Sunset Publishing, 1995). They have developed their own system of zones, which are much better suited to the mountainous western part of the country. The book will give you much more detailed information about growing in your region, taking into account rainfall and altitude.
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