Anyone know what's happening here? Deeply creased peaches, some with dark brown spots that are kinda gross looking. The tree is young, going on 3 years, so there's only a half dozen peaches or so (I also thinned a few). They're nearly all like this, except one (which tasted pretty darn good). I haven't tasted the weird ones yet because they're a bit underripe.

I'm in a hot inland valley at the outskirts of the Bay Area, CA (zone 9, but 90-100 degrees during summer). I'm watching my water use closely because of the drought (& no one likes watery peaches), so it's possible they're underwatered. Fertility & ph of soil are pretty great (I had a soil test done in the fall). There are no pests on the tree, though we did have a bad thrips issue in the spring (though I didn't notice any on the peach tree & minute pirate mugs eventually took care of the issue). There are no worms or anything like that in the peach that I cut open.

(just fyi, the green-ish peach in the photos was picked a few weeks ago, because I wanted to see what was going on. the other weird ones on the tree are coloring up like normal, but the crease is still just as deep & weird).