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Andricus quercuscalifornicus
Red gall on oak tree.about the size of a cherry.
On both of these choices you would have Andricus quercuscalifornicus, Amphibolips quercusjuglans is an eastern gall.
http://bugguide.net/node/view/507502
orbea,could be blue oak/or Quercus lobata. Will pay more attention next time.