Hello,

This appears to be a gall formed by eriophyid mites. Your picture comes out blurry on my computer screen. Would you say the red areas look slightly raised and similar to felt or velvet? 

 The Erineum velvet galls are  cosmetic galls  that do not harm the tree and are various colors.This year we have had many reports of these galls.

Once the gall forms in early spring there is no ‘ cure’ for the individual leaves. Because it is a cosmetic issue, there are no controls necessary. Here are some examples of how these galls change over the season- https://bygl.osu.edu/index.php/node/751

Populations of the mites that cause these  galls will vary from year to year, so perhaps next year you will see  less  damage. What you can do is keep your tree watered during the dry times, as we are having right now, and into the fall if rainfall doesn’t return then.  Keeping trees properly watered, without drowning them, is the best thing you can do for the health of your trees.