Thanks for the question.

We believe these are maple leaf galls. The bottom line is that they are harmless to the tree and should have no adverse effects. They are very common on maple leaves. They are caused by adult Eriophyid mites. In the spring the adult mites (they are extremely tiny) emerge due to eggs being deposited the previous year (2020) and start to feed on leaf juice. A most amazing thing then occurs. This feeding triggers cell growth on the leaf and leaf tissue grows around the mite. This plant growth is now manifesting itself in the galls that you are observing. At some point in the next month or so, the adult mite will dig its way out of the gall, mate, lay eggs, and the cycle starts all over again The current hypothesis is that this gall formation is a protective response by the plant. There is no harm done to the plant. The only response should be amazement and fascination by this wonder of nature. See the following:

https://www.gardeningknowhow.com/plant-problems/pests/insects/spindle-gall-treatment.htm

https://www.thespruce.com/dealing-with-leaf-galls-1402697 - :~:text=Leaf galls are a disturbing,, nematodes, and even viruses.&text=The gall itself is the plant's response to the irritation.

https://extension.umn.edu/yard-and-garden-insects/insect-and-mite-galls

https://apps.extension.umn.edu/garden/diagnose/plant/deciduous/maple/leavesgrowths.html

Thanks again for the question.

Glad that a gopher could help a badger