Pleasant Hill, Contra Costa County, California, USA June 16, 2011
Several oaks next to the Iron Horse Trail had galls like these, either singly or paired. The larger gall was 2.3 cm across, and a beetle was found on it:
Contributed by R. Berg on 17 June, 2011 - 12:52pm Last updated 26 June, 2011 - 1:33am