Ceanothus seems to be in bloom all over the city as I write (early April 2017). There are 50 or so speciesof Ceanothus, but very few that can be trained as a tree. Ceanothus 'Ray Hartman" is one - it's a hybrid (cross) between two parent species: Ceanothus arboreus from Catalina Island in southern California, and the northern California Ceanothus griseus. It’s the only Ceanothus planted as a street tree in San Francisco, and one of the very few California natives that you’ll see planted in sidewalk cuts on the street (along with Catalina ironwood).
These trees in Cole Valley at the corner of Waller and Cole are some of the best in San Francisco.
(And I wish I knew who this "Ray Hartman" was/is - doesn't seem to be any info on the web about him. Let me know if you know!