Its hard to tell from the photo(maybe closer would be better) but the leaves are not black. Fireblight usually starts at the tips of a branch then works it way down. The tip is bent like a shepards hook and the stem and leaves are black.
Ck your water. What kind of water system do you have? Did some one spray weed spray near by? Is that plastic over the roots?
Did you use fertilizer? Stockton can get pretty hot. Though I don't think it is weather related.

Consider verticillium or similar diseases as a cause of the individual branch die-off.

Hey there, here's a closer up picture. The plastic was only there for a couple of days. It is adequately watered with a garden hose, and no weed spray or fertilizer has been used. I'm actually starting to think it's weather related because it really is just that hot in Stockton right now. Though, I've never experience die back in any tree like this before.

OK, after a little research I believe it is Verticillum Wilt. Whew. Not canker. Mrs. G

Gee, I would say fireblight. Quince doesn't turn black like pears. Its also super-susceptible and is why my quince are now rootstocks. Note the "crook" on a few of those tips... a classic sign due to the sudden dieback.

I would say 80% probability of FB but it could be something else.

I would prune it all out to remove any spores left on the dead bits.

Scott

hmmm.. After looking up Vertiillum wilt, it does appear to have the same symptoms. I've just cut back all of the burnt leaves and hopefully it will return to normal. Thanks for all of the feedback