Where do you live? Can you cut the fruit open and show another pic? Got pics of the foliage? What does the bottom end of the fruit look like?

Whoops, my apologies. Santa Monica, but this was in West Hollywood. Zone 10b I do believe.

It looks something like a Limetta, aka "Sweet Lemon"

Did all the fruit on the tree look like that?

Hmmm.. Actually, not all of them. Many of the others were rather high up and may have been less mature/ripe, thus they were smaller from what I could see. It could have been a chimera tree with a few grafts of differing varieties?

Reminds me of the more wrinkly skinned satsumas.

FataMorgana

A Satsuma the size of a large grapefruit, Fata?

Can you show the top of the fruit (It appears to be upside down)?

Didn't see the size but it wouldn't be the craziest thing. My supermarket occasionally sees "sumo" clementines that look like grapefruit-sized satsumas.

FataMorgana

I will look for another today at lunch and get the top shot. Thanks for all of your help. I might be leaning toward the Satsuma, although this one is considerably wrinkly. The Limetta, although wrinkly enough, might be too pale and yellow to be this. Unless there is a variety that is more orange.

Could it be ugli fruit?

It looks like photos that I've seen of Bitter Orange (Citrus aurantium). Here is a WIKI article on that species.

I wish that it was Ugli Fruit! It seems to be too orange-hued, but the Bitter Orange seems to be quite accurate. Thank you. Has anybody had one before? I find that the taste is just like a fusion of the lemon and the orange.