It wasn't until I recently saw a picture of a related species from France that I realized Sara Orangetips have AMAZING hindwings.
Landed on me in the parking lot. Numerous valley oaks and coast live oaks nearby.
There were a bunch of these flitting around a mostly dry stream bed running through oak woodland. Somewhat tentative ID given that MPG doesn't have a complete set of photos for this genus in CA, but it's a good match for pics from BG and PNW Moths, particularly given the light-bordered reniform spot:
Mud puddling in a nearly-dry stream.