Dave
This is a banded alder borer. It is found in the western United States plus British Columbia and Alaska, from California and New Mexico north. Larvae feed in dead hardwood trees: maple, alder, oak, willow. It does not harm healthy trees.
These longhorned beetles are confused with the eastern Asian longhorn, but if you look at photos of the two, the banded alder has much more distinct black and white bands while the asian has spots that are not in a certain pattern. They are both in the Cerambycidae or longhorn beetle family.
Here is the banded alder beetle images - http://bugguide.net/node/view/8975/bgimage
Here are the Asian longhorn beetle images - http://bugguide.net/node/view/18855/bgimage
