The galls are on a couple of different white oak trees (Quercus alba). The first photo I uploaded shows a gall on the terminal end of a shoot of a very small tree (< 1 ft.). But I'm not sure what detachable means. I didn't try to detach any of these, but I took some photos from different angles - one of the same gall and one of a different gall in the middle of a stem. The gall appears to be wrapped around the stem in each case. I don't see any kind of distinct attachment device - just the fluffy outer covering.

Here is an example of a non-detachable stem gall:

I mainly wanted to verify that this wasn't a leaf gall.

Thanks for posting the additional photos. Galls of any given cynipid species typically grow only on one specific part of the oak tree. (There are some exceptions.) There are leaf galls, stem galls, catkin galls, bud galls, petiole galls... so knowing what part of the tree they are growing on is important for identification. Some cynipid wasp species also have 2 generations per year, one generation which grows on one part of the tree and the other generation which grows on a different part of the tree -- and the galls usually look completely different.

ps. I unlinked the 2nd two photos from the 1st one because they are different individuals. But they are still in the guide.