Hello, This fruit tree appeared in my father-in-law’s backyard in Enderby, BC and we don’t know what it is. The tree has large thorns and the fruit, when it ripens, is yellow and a little smaller than a tangerine (bit larger than a golf ball). Looking at images online, there seem to be a few possibilities. I have photos of it from now (early July 2022) attached. Thank you.
Prunus americana or American plum can have yellow fruits (though red is more common). There are other thorned plums as well.
Prunus americana is rare in this region and usually produces a low branching, vaselike growth habit with comparatively large-looking and long pointed, downward oriented leaves. I would expect the mystery plum to instead be something with an old world genetic background.