Fruit Tree Damage

This appears to be old borer damage several seasons old followed by sunburn and decomposition. It may be too old to see if you can spot any exit holes with sawdust-like frass. If you do see the holes that borers were the problem. Suggest you show this photo to a horticulturist at your local garden center or a master gardener at a nearby university cooperative extension service to confirm the problem. Or cut off the affected branch so that the horticulturist can identify the problem in hand. For more information about borers here are a couple of sites for you:
Bark Beetles Management Guidelines–UC IPM
www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7421.htmläó_
A long-time (naturalized) invasive bark beetle called the shothole borer attacks damaged branches and trunks of many broadleaved tree species, including fruit …
UC IPM: UC Management Guidelines for Peach Twig Borer on Peach
www.ipm.ucdavis.edu/PMG/r602300611.htmläó_
Jul 7, 2014 … The bluntly oval eggs are yellowish to orange and are laid on twigs, leaves, … Peach twig borer overwinters on the tree as a first- or second-instar larva … Peach twig borer can damage stone fruits by feeding in shoots and …