how do you know it's a moth and not a sawfly? It is very similar to but you're right the larva doesn't have that sawfly look with the big black eyes.

I'm 99% sure this is a sawfly gall, probably caused by Pontania sp. I can't be sure if the larger larva is the gall creator or not. It could be but I can't see details (like the number of prolegs or eye details) to be sure it's a sawfly larva. Lots of other critters tend to take advantage of galls ... clearly at least one of the larvae in the gall has taken advantage of the situation.

Ron Russo (p. 216) says of the gall caused by Pontania californica: "Caltagirone (1964) found a remarkable complex of inquiline, parasite, and hyperparasite species associated with this gall maker that included six wasps, a moth, and a weevil. In some cases, it has been found that the moth alone can account for as much as 70 percent of the mortality of the sawfly larvae."

I think it's safe to move this to Pontania (genus level), but I'm not sure what to do about the caterpillar image. I do think it's a moth larva, but in a sawfly gall. The Caltagirone reference would suggest a possible/probable ID, I suppose...

I'm pretty sure that sawfly larva have more prolegs than on any Lepidoptera larva? (From gardening web site - The (sawfly) larvae resemble caterpillars or foliage feeding cutworms at first glance. However, notice that sawfly larvae have 8 pairs of abdominal prolegs as compared to caterpillars, which have no more than 4 such pairs".) Maybe Joyce Gross will comment. I think this is probably a sawfly gall...

I remember clearly that mine had no "eyes" and share the same anatomical traits as caterpilars. Those images do make me think on another viewpoint, though.