Vine maple (Acer circinatum). Looks like autumn coloring to me - I see no Rust. It hasn't rained here for a month, your tree may be turning color and about to start dropping leaves in response to dry soil conditions. If this change does not go on to become blighting off of affected branches - particularly with leaves lingering on other parts of the tree - then fall coming early in this instance is probably all it is.

The other day I saw one that was already about half bright orange, with the rest in the process of getting there.

Early autumn color typically equals water stress.