Callirhytis carmelensis
This cynipid wasp induces glossy, mottled galls at the base of acorns of coast live and interior live oaks. I have not found them on California black oaks, even though they are recorded as occurring on this species.
They are maroon or green with light-colored mottling, and each has a small nipple at the apex.
Galls produce honeydew that attracts ants, bees, and yellow jackets.
”- Russo, Ronald A. : (2021) Plant Galls of the Western United States©