Never see gall like that locally, I'll search if they are other data and the host species present in the adjacent riverside forest. Finally host plant is Rosa acicularis that converge to be the good species!
Observe on a Prickly Wild Rose cane.
Preliminary identification for CNC 2024: Spiny Leaf Gall Wasp (Diplolepis polita). The largest of these measured ~8 mm in diameter. Photographed on the leaves of a California Rose (Rosa californica) at Stone Lakes National Wildlife Refuge in southwestern Sacramento County, CA.
Gall on rose (Rosa sp.)