Gall on Arroyo willow (Salix lasiolepis)
This gall is induced by a sawfly (Pontania californica syn. Pontania pacifica)
Bonita Cove, Marin Headlands State Park
Marin County, CA
If you think this observation is inaccurate, please add an ID, participate in the quality assessment above, or describe the inaccuracy in a comment.