So far it's basically a Japanese garden, you are saying you want to add California native plants to the same arrangement? If there is enough summer shade native woodland plants might be possible, and would look the most harmonious with what is already there. For the hummingbirds specifically Aquilegia formosa comes to mind.

Otherwise even if you change the rest of it out the maple will still want to be kept moist, not be in character visually with plants that look like they are from chaparral or desert in particular.

Whatever you do be sure to put taller evergreen plants behind and around the back of the fountain, to help create the illusion that there is higher ground above. Otherwise it will continue to appear that the stream is falling out of the sky.

You might have better luck posting on a CA gardening forum. I can't help much with native CA plants that attract hummingbirds. They love water though . . .