Now that you say it, I definitely see the walnuts in the background. I looked in 'Field Guide to Plant Galls of California and Other Western States' by Ron Russo, I think Eriophyes brachytarsus looks promising. Here are some other references.
http://smu.gs/1c8jk3W
http://bit.ly/JuUxwB
What's the host? Willow? To be blunt, this is not even close to Callirhytis quercuspunctata which is an eastern gall on oak.
http://bugguide.net/node/view/255247
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