Based on the host oak section and the appearance of the gall, Dryocosmus is a very unlikely generic assignment for this gall; Druon seems plausible. (Keep in mind that the 2022 paper re-establishing Druon came out after Russo's field guide was published.)

Russo lists the host only as a "hybrid white oak" found in the Santa Rosa Mountains; Q cornelius-mulleri is added as a placeholder, as the most common white oak in the area.

This gall was observed on Quercus cornelius-mulleri in California in April.