There are so many different types of goldenrod galls! They are made by insects that induce abnormal growth of the tissues of the plant, providing protection and food to the gall maker and no benefit to the plant. Not only that but there are many parasitoids and inquilines, a whole series of ecosystems with very complex faunas.
Here are some of my photos, comments and links to information on goldenrod gall fauna.
This type of gall is caused by a small fly, a gall midge. Each small gall is like a blister in between two leaves of goldenrod. Inside the gall the midge larva grows surrounded by food and seemingly in safety.
The safety is only an illusion. Quite often the galls are parasitized by tiny wasps that end up killing the larvae of the gall maker.
This is one of the parasitic larvae.
List of articles