Triodanis perfoliata; Campanulaceae (bellflower family) [formerly Specularia perfoliata in the lobelia family]
It’s the time of year when blue and purple take over, or so it seems. Look at what I’ve posted recently.
This is a pretty plant, standing about one foot tall (sometimes taller), always single-stemmed, and with flowers appearing singly in the leaf axils. It prefers dry, nutrient-poor soils; in this area look for it along rocky bluffs along the edge of the river. It’s found in every state in the US except Nevada, and in most of Canada.