These fruit are fully ripe in northern California in the first few weeks of September. They are very bitter until they turn almost black then they taste mildly sweet and plumb-like (only tasted, not ingested till ID'ed). They are the size of cultivated cherries.

Notes: The fruit is growing on racemes. Stones very large for fruit size. Leaf edges have no serrations.

So far looked into it being the species below but it appears it probably is not any of the following:

Prunus laurocerasus (because we have this species on the property as well).

Prunus lusitanica - very different leaf. different fruit shape.

Prunus virginiana (fruit of this tree is much smaller than the ~1 inch fruit we see on our tree)

Prunus serotina - very similar but no serrations on leaf edges

Prunus caroliniana - leaf edge doesn't match no serrations

Prunus padus - leaf edge doesn't match no serrations

Thanks for any help!