Rare Bird: Dark-eyed Junco (Oregon)

One of the slate-colored juncos was a Cassiar junco. Seen foraging on ground and in small shrubs with flock of slate-colored dark-eyed juncos. Distinctive dark black hood covering head and neck, well-delineated from grayish flanks/ back and whitish gray breast but no chestnut or reddish flanks as in true Oregon junco. Matches field guide pictures of adult male Cassiar junco but could be Oregon slate-colored hybrid?