Officially Philadelphus lewisii; can I say “Philly Lew”? Out here in Pacific Time we call it “Native” because it is.
This picture is a little misleading, suggesting that the blossoms occur in small numbers posed in a fetching Zen way against the dark foliage; but in fact they occur in thousand-strong masses all over a ten-foot-tall (and growing) shrubbery.
Camera-geek note: This is (I know it’s getting boring) yet another 40mm Pentax Pancake Prime shot. It’s totally the greatest lens I’ve ever had.