Ask Mr. Smarty Plants

According to this USDA Plant Profile map, Acer negundo (Ash-leaf maple) is native to Shasta County, in north central California. However, according to this Arbor Day Foundation website, what you have is a cultivar of Acer rubrum (Red maple) which, according to this USDA Plant Profile map, is native only to the eastern half of North America and not in California at all.

We like to check on whether or not a plant is native to the area in which it is growing, because if it is not, that could explain the problems the plant is having. However, in your case, this appears to be a problem with this one tree out of nine. A tree only two years old could certainly still be vulnerable to transplant shock. We're assuming that all your trees were planted at the same time and in the same manner, so if just the one has transplant shock, it must hark back to something that happened before or during the planting of that particular tree. The trees roots may have been rootbound when you bought it, and if they were not clipped to open up the root system, the roots could still be wrapping around in the shape of the pot and strangling the tree.

This Southern Living article on 'Autumn Glory' recommends it highly but also mentions transplant shock and root strangling. It is very difficult to correct errors made in planting. One possibility is that the roots of that tree have poor drainage, in which case the yellowing of leaves could be due to chlorosis. You could attempt a fix on that by adding an iron supplement to the soil around the suffering tree. Root damage may be preventing the new rootlets from accessing minerals and nutrients from the soil. Don't overdo it and treat only trees showing that symptom. Chlorosis is more likely to show up in alkaline soil but, again, if the other eight are all right, your soil is probably right for the maple.