While leading a tour in southern Grant County, Oregon today I found this bird which appears to be a MacGillivray's Warbler x Common Yellowthroat hybrid. Its call notes were a bit harsher than MacGillivray's Warbler, but its song was typical for that species. Since songs are learned, this isn't surprising.
The location was along Jack Creek Road east of Bear Valley. This road is the continuation of Scotty Creek Road, not long before it joins up with the paved Izee Highway.