A redwood? I presume Coastal Redwood, Sequoia sempervirens? And lots of shade.
Does not sound too good for most Californian natives.
If you have ever been in a redwood forest you will discover that there is not all that much diversity there. Lots of ferns, mosses, and other species, mostly found in breaks in the forest canopy! Unless you are talking about the bryophytic flora which may have the best diversity of species for this particular type of plant community.
What you need to do is to open up the canopy by trimming back the redwood, working up the substrate (not immediately around the tree), adding some grit, such as decomposed granite (found at landscape yards-maybe in your area??),
and decide to dedicate time to maintaining and updating the area throughout the year. I would think the easiest approach is to use seeds, possibly annuals, that could be planted throughout the year and allow a meadow to develop, perhaps adding some water element(s) to the scene as well as small but noticeable boulders, and harvesting off debris after the plants have seeded (or even collecting to store) has been completed.
Controlling watering patterns could actually be tied to actual precipitation events in a similar area of California by tying in weather.com or accuweather.com. For seeds the Theodore Payne Foundation offers a broad selection to work with:
http://store.theodorepayne.org/category/SEED_M.html