Link to host plant, California Goldenbush (Ericameria ericoides) observation: https://www.inaturalist.org/observations/208027635

Rosette-Bud Gall Midge (Rhopalomyia ericameriae) This midge induces rosette bud galls with flaring and slightly recurved bracts on California Goldenbush and Palmer’s Goldenbush. At first the leafy bracts are erect, but they recurve and turn brown with age. These galls measure 7 mm long by 5 mm wide and are green when fresh. Bracts are 1–2 mm wide. Larvae develop during the spring and early summer.
Midges are small, two-winged flies. Midge larvae pupate inside the galls. Adults emerge in April to oviposite in new buds.

Plant Galls of the Western United States: a photographic guide to 536 species of plant galls found west of the Rockies, with 400+ color images and plates, Ronald A. Russo, April 2021. (Available on Amazon), p. 259, pl. 445.

Gallformers: https://www.gallformers.org/gall/2288
"Rhopalomyia ericameriae, Family: Cecidomyiidae | Genus: Rhopalomyia
Hosts: Ericameria ericoides, Ericameria nauseosa, Ericameria palmeri
Detachable: detachable
Color: brown, gray, yellow, green
Texture: leafy
Shape: rosette
Location: bud"

Gallformers shows 2 possible (insect) galls that occur on Mock Heather (as of 4/18/24): https://www.gallformers.org/id?hostOrTaxon=Ericameria+ericoides&type=host&detachable=&alignment=&cells=&color=&locations=&season=&shape=&textures=&walls=&form=&undescribed=false

I.D. Galls. Select "Identify" and type the host name: https://www.gallformers.org/id

Galls. https://www.inaturalist.org/projects/galls-of-california/journal/44203-where-to-learn-more-about-galls

There are multiple stem-based Oak Galls in this Coast Live Oak tree. These galls are also abundant throughout the park. It's the gall on the left in photo 13.

Host plant: https://www.inaturalist.org/observations/195900646

Photos 2-5, 8-11, and 13 were edited to have a Custom White Balance in Photoshop (Photoshop's preset).
Photos 5, 8-11, and 13 were darkened.

There are multiple stem-based Oak Galls in this Coast Live Oak tree. These galls are also abundant throughout the park.

Host plant: https://www.inaturalist.org/observations/195900646

Photos 2-5 were darkened and edited to have a Custom White Balance in Photoshop (Photoshop's preset).

There are multiple stem-based Oak Galls in this Coast Live Oak tree. These galls are also abundant throughout the park. This one has many exit holes.

Host plant: https://www.inaturalist.org/observations/195900646

Photos 1-4 and 6-10 were edited to have a Custom White Balance in Photoshop (Photoshop's preset).
Photos 1-8 and 10 were darkened.

There are many Two-horned Galls in this Coast Live Oak. They're on the underside of the leaves along veins. This one has no holes and is on a smaller vein.

Host plant: https://www.inaturalist.org/observations/195900646

These photos were edited to have a Custom White Balance in Photoshop (Photoshop's preset).

There are many Two-horned Galls in this Coast Live Oak. They're on the underside of the leaves along veins. These have no holes.

Host plant: https://www.inaturalist.org/observations/195900646

Photos 2-4 were edited to have a Custom White Balance in Photoshop (Photoshop's preset).

These galls remind me of powdered donuts...

There are many Two-horned Galls in this Coast Live Oak. They're on the underside of the leaves along veins. No exit holes.

Host plant: https://www.inaturalist.org/observations/195900646

Photos 3-6 were edited to have a Custom White Balance in Photoshop (Photoshop's preset).
Photo 5 was darkened in Photoshop.

For the small green gall.

There are many Two-horned Galls in this Coast Live Oak. They're on the underside of the leaves along veins.

Host plant: https://www.inaturalist.org/observations/195900646

The larger gall next to it: https://www.inaturalist.org/observations/204824999

These photos were edited to have a Custom White Balance in Photoshop (Photoshop's preset).
Photo 4 was darkened in Photoshop.

There are many Two-horned Galls in this Coast Live Oak. They're on the underside of the leaves along veins. This older gall has 1 exit hole.

Host plant: https://www.inaturalist.org/observations/195900646

The adjacent green gall: https://www.inaturalist.org/observations/204825005

Photos 2-7 were edited to have a Custom White Balance in Photoshop (Photoshop's preset).
Photo 7 was darkened in Photoshop.

There are many Two-horned Galls in this Coast Live Oak. They're on the underside of the leaves along veins.

Host plant: https://www.inaturalist.org/observations/195900646

Photos 3-8 were edited to have a Custom White Balance in Photoshop (Photoshop's preset).
Photos 6-7 were darkened in Photoshop.

There are many Two-horned Galls in this Coast Live Oak. They're on the underside of the leaves along veins. This gall has 1 exit hole.

Host plant: https://www.inaturalist.org/observations/195900646

Photos 1 and 3 were edited to have a Custom White Balance in Photoshop (Photoshop's preset).
Photo 3 was darkened in Photoshop.

There are many Two-horned Galls in this Coast Live Oak. They're on the underside of the leaves along veins.

Host plant: https://www.inaturalist.org/observations/195900646

Photos 1-4, 6, and 11-12 were edited to have a Custom White Balance in Photoshop (Photoshop's preset).
Photo 6 was darkened in Photoshop.