The title should say dwarf.

Last year was the first time I had a few fruits. Boy they were good.

This year my little tree has quite a few fruits. I went out to water today and was shocked to see this (see pic)

I googled the issue and came across this info from the University of California Agriculture and Natural Resources.

Navel Orange Spilt

http://homeorchard.ucdavis.edu...

I removed three fruits. I hope I don't get more :(

What a shame. Did you get a sudden douse of rain lately? - I know, that seems like a silly question given that you are in California.

Our citrus trees here have their root systems very close to the soil surface, so any sudden rain or increase in watering is absorbed quickly, which according to your excellent article might have been what happened.

To prevent this happening again, I would apply some mulch to the root area, to help keep the soil moisture more consistent. Spread it thick, and out at least a foot beyond the reach of the branches (drip line) because the feeder roots go out that far. Then be sure to water as regularly as you can for the same purpose. The only caveat on the mulch is to keep it away from the trunk 6in. or so. Here we get trunk or foot rot easily if the trunk of the tree stays too wet. Again that doesn't seem too likely in CA, though.

Sorry about your oranges. We experience that here in Arizona too with sudden changes in temperature or humidity with our thinner skinned citrus. Not so much with our lemons or grapefruit.

Our weather has been wacky.

I noticed my mini watermelon has rot on the bottom too. :(
It's the first time I've planted watermelon. Lots of vine and
flowers but not much fruit. I sometimes wonder if it's worth
the water since we are having strict water restrictions.

Probably right, melons take a lot of water in proportion to the harvest you'll get. Best to let someone grow them for you where there is enough water to size them up. Especially watermelons are water hogs, and then you're growing a lot of rind that you won't eat, too.

You could probably grow Dragon Fruit really nicely there - they grow on an epicactus, don't need a lot of water.
Dragonfruit (Selenicereus monacanthus)

"You could probably grow Dragon Fruit"

I do have one! It's in a hanging basket in the far back yard. For awhile it looked like it had some type of disease but I think it was sun damage. I cut all the damage off and it looks pretty good. Several of the "arms" have what looks like roots growing out of them. I'm thinking maybe I can root them and make more plants?

I looked at a youtube video someone posted here about dragon fruit and the little roots aren't roots but aerial roots! I am always learning something new from you all!