One more photo here...this picture you can see the yellow colored one near the top right half...i just touch those and they fall to the ground...

Although Santa Rosa is supposed to be self pollinating, you'll get much better fruit set, if you have another variety that blooms at the same time.

Scuzzy- Did you get a late frost? Santa Rosa, and Mariposa were more susceptible to late frosts than sweet cherries for me, so I removed them.

Thanks for the replies.

No frost, I live in Southern California. There might have been frost ONE morning, but that's it. It blossoms really well, like i said probably more than 200 blossoms. Just don't know why all the fruit is falling off, there's probably 10 left of the 50. Most of them turned yellow and fell off...

Any one else have any further feedback on why most of the fruit have fallen off and turned yellow? Thanks for any help...

Not a whole lot to go on. Most likely a pollination issue, but could also be lack of -or too much water and/or fertilizer. How old is the tree? Did you see much bee activity when in bloom? Can you attach a full picture of the tree?

I have one too, (I live in SoCal) I am having the same problem.

The reason is that they didn't get pollinated. They need a pollinator: Satsuma, Mariposa, or a Prunus vesuvious cherry-plum, these trees pollinate my Santa Rosa.

S...my trees in SoCal flowered...set much fruit....dropped much fruit. I have grown these plums and others for many years. I can assure you this is a weather related problem, not pollination. We had a cold late Winter/Spring.

There's too much data on Why Do Plum Trees Drop Plums & Never Develop? to dismiss pollination as a possibility. A "weather related problem" in and of itself is tied directly to poor pollination - as it impacts pollinators greatly.

I have one which dropped most of its flowers and I blaming the frost. The remaining 15 fruits are big and healthy . My job starts now to protect the 15 fruits from the OFM. In mid-Atlantic states it is a big problem.

My small Santa Rosa Plum has dropped the few embryonic plums it had produced. Every one of them. It is a young tree and I may have over watered it. I am near the ocean and that poses some interesting gardening issues from time to time. So far nobody has come up with a solution to the problem, so I guess I'll withhold the water for awhile and hope for the best.
The Apricot tree next to it is "leafing out" beautifully -- it's second year -- hopefully it will start producing some fruit this year.

This is in reply to the first poster, ..at this stage, going by the size of fruits,
it doesn't look like a pollination issue, more like a pest, could be plum curculio damage.

Setting fruits is another problem and I find that it's a fine line from setting or not setting,..in your case James, tree might still be too young.

I think immaturity of the tree also has something to do with your tree not setting fruit well.

I planted my Shiro in 2012. Last year, it had a lot of blooms, most friutlets turned yellow and fell off. Only A dozen plums left to ripen. No pollination issue for another J. Plum is next to it.

This year, it flowered and set in hundreds. Lot of thinning requied. The tree knows last year it was too young to carry lot of fruit so it aborted most.

I think your tree will be fruitful next year if your have a compatible plum tree nearby to cross pollinate.