Hello,

Thank you for reaching out to Ask Extension with your question!

Based on your description, I am thinking that you have some pesky squirrels that are causing this damage. They can be a nuissance to our trees, and are typically the culprit when you find little gnawed off twigs under a tree.  Here is more information:

https://planttalk.colostate.edu/topics/wildlife-issues/2303-squirrel-damage-trees/

You also mentioned galls which are caused by a myriad of insects. Galls are more of a cosmetic issue. It does not usually harm the plant and treatment is not normally necessary unless the problem is severe.  Here is more information about galls and the insects that cause them:

https://extension.colostate.edu/topic-areas/insects/insect-and-mite-galls-5-577/

I bet you have a plump and happy squirrel dining on whatever insect or mite is making your galls.

I hope this helps,

Dawn