I knew immediately by the shape of the nest that it was an oriole nest, and my suspicion was that the Orchard Orioles we had been hearing and seeing had built the nest. Orchard Orioles usually nest in trees in riparian areas, but they are also known to nest on farms and in parks.
Today, I caught the female in the nest. You'll probably need to click the photo below to see her in the nest.
I have some concerns about the location of this nest, as the branches to which it is attached blow around quite a bit in the wind. I'll keep an eye on the nest, and hopefully I'll have the chance to post photos of young Orchard Orioles soon.