Hard to tell the initial cause of dead limbs by what you have described. However if you dont remove the dead portions of the tree it is going to cause more damage to the living tree eventually.

That looks typically of cold injury which I see often in the cold north. Cut these limbs off, tree will shoot out new one's and you'll end up having a rejuvenated tree.

You guys are much more learned than this SoCal boy regarding cold injury. Around here that look can be caused by borers. Look for little holes in the bark. Regardless, follow the above advice and cut out all bad wood.

I was figuring winter injury, but wasn't sure. I'll remove the big dead branches. Thanks!

Now should I do the same with the peach tree that's right next to it? It has the same issue of only blooming on one side and being brittle/dead on the other. It doesn't have a split open branch like the apple tree though.

Also, can any suggest a fertilizer for the injured trees?

If dead then cut,..I wouldn't put down any fertilizer this year since you cut limbs off, freeing up allot of energy, [not needed anymore] thus pushing out new vigorous water sprouta. Only use fertilizer when you see not growing well, dress with some compost or old manure.