Answer: The contributing factors to the creation of microclimates are elevation, bodies of water and valleys, so your observations are correct. Even though you have been placed into the broad USDA category of zone 4, you may actually be much colder or much warmer than the average low winter temperatures for that gardening region. A more reliable source of zone identification for you might be from Sunset Western Garden Book. The authors have researched the elevation and proximity to water for all areas in all of the western states and place you in their zone 2. This is the second coldest western climate with annual low temperatures ranging from -3F to -34F.
With this in mind you might want to consult Sunset's Western Garden Book for plant suggestions and a thorough explanation of their climate zones. Most gardening outlets and library's have copies of the book. (ISBN# 0-376-03851-9)
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