A common tree along the banks of the San Gabriel River. I've added observations of this before (e.g.,http://www.inaturalist.org/observations/1800378) but still haven't figured out what it is.
Night photos. First three images, ambient artificial light. Fourth image, flash-illuminated.
Wingspan: approx. 10 mm. Measured in situ with caliper.
Possible: Leaf Cutter bee(Family Megachilidae) Megachili species