I found this beautifully structured nest in chaparral habitat. It appeared to have two compartments, one of which had been opened (as seen in the third picture). I found this single -- but very helpful -- similar-looking image which has been identified as the nest cell of an Anthidiini species:



The stem I found it attached to was quite dead and as such I'm not certain what species it may have been originally. Typically, that area is densely populated with Mustard (Brassicaceae) plants and I suspect that is what this may be, but am not certain. When things begin to bloom again in Spring, I should have a better idea...

In addition to getting an ID confirmation for the builder of the nest, I'd be curious to know when it is most likely that this nest was constructed? One of the cells seems to be unbroken and I'm wondering if it is still possible that something will hatch at this late stage?