The wasp is Pseudomasaris vespoides.
Pair of them in an Oak tree.
Brief description of what you observed
Buck and several does with no intention of sticking around for a photograph.
On blue oak.
On valley oak.
Small colony on rocky cliff.
On California buckeye.
Observed several flocks. Hiding in chaparral vegetation.
In live oak.
Several heard and observed.
Invasive, spent heads.