The male Western Tanager (Piranga ludoviciana) is unmistakable. He is the only tanager with strong wing bars, the anterior wing bar (median coverts) being bright yellow. Click on photos for full sized images.
The female, this one spotted in my yard last September during fall migration, is a bit tougher to identify. She has kind of an olive-grayish back and scapulars with a greenish-yellow nape and rump. From this photo you can see she has a whitish belly but yellow undertail coverts.
They range farther north than any other tanager, arriving in California to breed usually in May.
We spotted this male at Lassen Volcanic National Park last weekend where the Western Tanager nests, usually 20 feet or higher in a conifer.
Gotta love that flaming red head.
And a look from behind.