I thought this was a Monkeyflower. However, I recently found a Common Yellow Monkeyflower and realized I may have misidentified this flower. The attached photo is the only one I have, so I don't have any recollection regarding the leaf pattern.
Thank you Ron. Images on CalPhoto and Google suggest it is Linaria maroccana. Interesting that it showed up on a Southern Oregon hillside of mixed white oak, madrone and ponderosa pine. Again thanks for the ID.