On our last visit to the Gamble Garden in Palo Alto, we came across an impressive cluster of thick stems (clearly some years old) standing about 3 feet tall, with conical clusters of buds at the top of the stems. The only label we could find was for an obviously irrelevant plant (a daisy-like composite).
But then this morning we went back, and it was in gorgeous purple-blue bloom. Back home, I thought to try a strategy that almost never works in Google searches: describing the plant (“tall spires of purple flowers”), but this time I hit paydirt right away, with a page devoted to plants with tall stalks of purple/blue flowers. Echium candicans aka fastuosum: