I can't remember seeing one of these before in San Francisco. My husband took me this past weekend to his new favorite dog park (our dog Mather, named after the San Francisco Sierra camp, needed a run). It's a flat area in Corona Heights Park that you can access either from State Street or from Flint Street. (If you're approaching from Flint, walk past the tennis courts; if you came up the driveway from State Street, walk past the basketball courts.) You'll come to a dog park adjacent to some community garden plots. - and in between the two, this Dracaena draco - the common name is Canary Islands dragon tree.
The plant (not really a tree - it's a monocot with a tree-like growth habit) is native to the Canary Islands, Madeira, Cape Verde and western Morocco. There's a beautiful example of this tree at the Hotel Coronado in San Diego; the two largest in California are both in the Santa Barbara area - one at the Sotto il Monte Estate in Montesito, and the second at Mount Calvary Monastery behind the Santa Barbara Mission. in Santa Barbara. But you don't see them often this far north. I'll actually be in Madeira in two weeks, and will update this with new photos if I see some!