Saltbush (Atriplex Brewerii) galls at Portugese Bend

Atriplex lentiformis Breweri (also Salt Bush, Quail Bush, and formerly Atriplex Breweri) grows abundantly on the Palos Verdes peninsula.   Out on a hike the other day I noticed what appeared to be galls on it:

I've been increasingly interested in galls, since they are an obvious and durable signature of the presence of wildlife.  Galls are often thought to arise from a nesting insect.  Chemical interactions between the insect and the host plant give rise to the gall, which hosts the insect's young.  If one bothers to think about it at all, then one might think of oak galls which are often caused by the sting of a native bee or wasp.  According to an article I recently read, there's a fascinating and complex interdependence between plants, gall-causing insects, gall using opportunist insects, and insects that prey upon the previous two kinds of insects.