found lots of different oak galls (all of them on valley oak, Quercus lobata) this morning while i was out walking with zane. galls are caused by tiny cynipid wasps. the wasps lay their eggs on the oak trees' leaves or stems and in doing so trigger a reaction that causes the tree to create a gall around the egg where the larva will then develop.
here are some links with more photos and information:
and here is what zane and i found this morning...