Today I found it (or possibly a different bird, hard to know for sure) in a tree near the Bodega Marine Lab facilities. This is only the second record for Cape May Warbler in Sonoma County (the last was on 9 June 1977 in the trees near the Bodega Marine Lab housing area).
It was very active, moving around in the upper levels of a Myoporum tree. But I think you'll be able to see most of the important field marks in these photos.
Look for the yellow throat and underparts, with extensive dark streaking on the breast and along the sides (hence the species name, tigrina = tiger-striped). The face is also yellow with a gray ear patch.
In the photo above, note the gray crown and the slightly decurved bill.
Below you can see hints of the white wing patches. The uppermost one is pretty thick (like a white smudge), making me think that this could be an immature male (females have two narrow wing bars).
And here's a back view with the olive-green back and a tiny glimpse of the yellow rump. This bird seemed very interested in the Myoporum flowers.
Cape May Warblers nest in boreal coniferous forests in Canada and the northern United States from Minnesota east to Maine. Their main wintering area is on Caribbean Islands. This bird is a long way from there right now, but it sure was nice to see it!
P.S. Photos of the individual observed on 26 September are posted here. Take a look and see if you think this is the same or a different bird. (Beware there's one Blackburnian photo in the set.)