Looks like a hack-berry (Celtis).

Hmm, but I've never seen a Sugarberry (Celtis laevigata) with such glossy leaves before?

Nor have I.

Could it be a Rhamnus instead? There are also several shiny Ceanothus, like velutinus, but I don’t think that’s what this is.

Sugarberry might grow shinier during warmer winters. They are much shinier the further south you go. The lowest low this winter was quite warm.

Follow-up here...I believe these are Jujube trees! What a surprise!

I thought of that tree also, was still thinking of it when I came back to this thread just now - and at this stage the fruits definitely provide confirmation. Maybe I ruled it out before because of the example shown having presumably come up on its own.

Ziziphus jujuba (to prevent future confusion). :-)