My CA live Oak - The bark has turned black and brittle.

Mark - I do not see your location, are you in an area that has infestations of Sudden Oak Death (Phytophthora ramorum)?  If so, and if indeed your tree is infected, I fear there is little that can be done.  Your county extension office would be a great place to start.  I would separate this tree from all others until you know for certain what this is.  And sterilize any tools you have used to work on it.

David B.

And, keep it away from any azaleas you might have!

Edit: Move to pests forum, where, if you search for Sudden Oak Disease, you will find more info from Nina.