What kind of bug is this?
Thank you for the excellent images of a native longhorn beetle, the banded alder borer,the technical name Rosalia funebris.
These beetles lay their eggs on the dead branches of certain tree such as alder, maple, oak and willow. In spite of their large size, they do not damage people, pets, or structures.
See "What's big, black and white, and not a pest?" at http://blogs.oregonstate.edu/treetopics/2011/08/26/whats-big-black-and-white/.