I have a small property in Arnold, California and I've had a huge problem over the last few years with a disease/pest on my cedar trees. The bug/larvae develop under the bark surrounded by a white sap/fungus. (seen here in left picture with the dark amber shell) The bark turns black and falls off (Middle picture) and the tree dies branch by branch from the ground up. (Right picture). It has killed a bunch of smaller trees over the last few years but has now started to kill my larger trees.

I've contacted a bunch of tree "experts" and arborists but no one can tell me what it is. Would really love if someone could identify it and, better yet, help me get rid of it.

I have more pictures if that would help.

Appreciate any help you can offer.
Regards,
Colm