These aren't great photos--I posted them because I couldn't find anything that looked like this in the guide. And, as usual, once I had them all posted, I figured out what it was. Why can't I find these things before I go through the work of posting the photos?

One possible reason is that adumbratus seems rather variable--but the adumbratus that looks most like this one is the one posted from Valley Center, which is less than five miles from my house as the crow flies. I guess the variation may be rather geographical!