Sambucus nigra caerulea
Blue elderberry. (formerly Sambucus mexicana, formerly in the Caprifoliaceae (Honeysuckle) family).
The “blue” refers to the color of the berries (which are blue-black), not the color of the flower.
Can bloom year round, probably peaks in March/April and then trails off over the summer. Seen on many trails, and all over town. The Wilcox property (Douglas Family Preserve now) has many large plants.