Raining black stuff from branches no smell from oak tree
Can you tell me what kind of tree this is?
It was stated in the subject line but it is an oak
So it does! My apologies.
My first thought was drippy blight which affects oak trees. However, looking more closely it really looks like animal waste. I know you said there were no birds in the trees, but doesn't look like any pest that I am familiar with. With that said, I've just realized that you are based in CA and there might be something out there that I'm not familiar with (I'm in CO). I suggest you contact your local County Extension office to see if they can help you figure it out http://cesonoma.ucanr.edu/about/contact/