A good number of these were flitting around on the sandy shore of the river, bounded by a low levee to the east...and acres of dense arrowweed (Pluchea sericea) beyond.

But, as usual, they were very wary and difficult to photograph. Another individual from the population appears below (I think it's the same species, though it has conspicuous longitudinal vittae on the scutum that seem to be absent here):