Gall found on the ground - Andricus quercuscalifornicus -
Trail in Stanford University Campus, Palo Alto County, California, USA October 25, 2015 Size: ~5 mm
Gall cut open. It had two Andricus quercuscalifornicus development chambers, next to each other. But only one adult in one. Unfortunately, I damaged its wing.
Note on the left section the abdomen of the stonefly larva is visible.