It's the wrong time of year to transplant it now. Best wait til it's dormant(leafless) next Winter.

Thanks saltcedar for the advice. Do you know what kind of tree/plant it is?

It's in the subject line above :-)

oh my! Good to know, thanks saltcedar, I see the subject now. :) We'll need to get rid of this tree as we have a nut allergy in the family.

In CA I would think it would be more likely to be an ash tree seedling. Believe me, you still want to get rid of it. And keep an eye out for other volunteers. If a neighbor has a seeding tree, there will be many more. If you wait too long, the taproot is a killer to get removed. Yanking them when they are no more than 5-6" will make your life so much easier.

Thanks Gyr_Falcon, I'll take your advice and get that out of there!

Yes it's a trash-ash, Fraxinus uhdei. I pull them out all the time.