I looked through every species in this genus on Bugguide, and a photo of a female of the species looked very similar to what I observed. I am no expert on potter wasps and would love someone to correct or to confirm this ID.
@matthais22
Near Big Slough on Auto trail. Little colony in open area, mostly grasses. Recently burned. Fleshy leaves. Looks like fruits forming. Larger clumps photographed are little over 2" diameter. Some individuals with one flower adjacent.