Aphididae

Stegophylla

Quercus agrifolia

California

Quercus berberidifolia

Quercus douglasii

Quercus garryana

Oregon

Washington

British Columbia

Quercus kelloggii

Quercus lobata

Nevada

Quercus wislizeni

Stegophylla essigi

Fundatrices feed as larvae near the edges on the upper sides of young leaves, which edges turn upward and fold over the insect. These folded marginal pseudogalls develop thickened, stiff walls, and usually turn red. In Berkeley, fundatrices were mature on April 1, and began producing young a few days later. In late autumn, I found colonies only on the undersides of leaves, more or less exposed, and only on evergreen oaks, with very few oviparae ... Swain (1919) recorded colonies from both the upper and undersides of leaves in summer, this has also been recorded for other Stegophylla species.

Notes on California aphids, with descriptions of new genera and new species (Homoptera: Aphididae)

A Field Guide to Insects and Diseases of California Oaks

Stegophylla essigi is a woolly aphid,  known only from the West Coast, that creates leaf fold galls on various native California oaks. The leaf margins--at least those on coast live oak in the photo in Swiecki & Bernhardt (2006)--are folded upward and become reddish. However, there are other aphids that make leaf roll/fold galls on California oaks. Further, Cecidomyiidae larvae in have reportedly been found in Quercus agrifolia leaf folds. 

Gallformers ID Notes