are they yellow dots on the leaves itself, or tiny yellow eggs? hard to tell from the pics.

Looks like some kind of rust. What kind of tree it is?

they are dots. I had this problem last year and when I described it to the guy at Fannicks, he thought it was bugs (maybe aphids, I can't remember now). The tree did fine through the winter but this problem has returned. it's otherwise healthy.

I thought it was a Mexican oak, but my new Mexican oak looks a bit different. (We got a few free saplings that year and I got mixed up which was which).

I do think it's a Mexican White Oak http://www.cpsenergy.com/images/GS_trees.jpg

I take that back, now I see the difference in the leaves...my other tree is definitely a mexican white oak. I think this one maybe a Texas Live Oak?

Looks like rust to me too. Is there a lot of leaf litter under the tree? That's not a live oak, leaves are too large.

No leaf litter.
hrm, it's definitely from that CPS list. What else could it be?

Were ther any pear trees on your list? Here's what a live oak looks like, courtesy of Treeland Nurseries.

{{gwi:1350942}}

SOmeone on the tree group said it was Quercus polymorpha
(Net-leaf white oak), and the images I found look right. I didn't think that was very common here, kind of funny they were giving them away and they weren't on the list if it's not even common in local nurseries (CPS gives away free saplings of native trees every Earth Day - we got this one about 5 yrs ago). The site I found says it's only found in Val Verde County.

They also suggested a mite may be doing this.

Ok, I finally got it....another name is Monterey Oak, which sounds like what I remember :)

Back to the original problem, I will look at mites and rust. Thank you!