Plant ideas for CA foothills spot?

I have some half-baked ideas about cleaning up a weedy area by my garage, inspired by the fact that I am looking for a place where I can relocate my mint patch ASAP. I was going to sheet mulch over the mint, because it is taking over part of my garden, but I would like to save it.

We are in the California foothills at 2500', with black oak, madrone, and Ponderosa pine. Most of the yard has sparse patches of nonnative grasses coming in, more every year, under the oaks. Very weedy-looking, and, yes, I realize that is definitely in the eye of the beholder.

Anyway, one area I would like to clean up and replant is next to our garage. The part right next to the parking area has a shallow ditch where water drains off the drive in the winter, so it can be quite wet.  The first photo has the front of the garage on the left, and the ditch draining the driveway straight ahead. The tall grasses fill the ditch area. There are also a bunch of thistles, which are on slightly higher ground. I would like to replant these areas with something edible, perennial, and more attractive to me. Our summers are dry, so the ditch area is very wet in winter and dry in summer. (Though we did have a very late spring this year, so the grasses in the ditch still have some green at this point.)

What can I plant in the ditch itself? Of course, the grasses do a good job of slowing down the water, so I like that aspect. Could mint live in this area? Or maybe native grasses? Any other ideas? Or maybe I should replace it with rocks to slow the water.

What small tree or large bush could replace the thistles? The corrugated metal walls in the corner face south and east. (Second photo is looking due north.) I'm not sure how many hours of direct sun it gets per day. I am guessing 3 or 4, with dappled shade the rest of the day. This could be the other location for the mint. If it then fills the ditch on its own, that's okay. I don't think it will spread too far beyond the watered area because it is so dry here in the summer. And if it does, that's okay.

How's about cover cropping it? Smother out some of the thistle family, fix nitrogen, green matter. An edible cover. Perennial rye? How's about a ferrocement bed (so you can shape it to the space specs) with culinary herbs perhaps?

http://milkwood.net/2010/11/08/how-to-make-ferrocement-garden-beds/

http://sustainableseedco.com/Organic-Dark-Northern-Rye.html

Mint would do well there. Berries, maybe? If it gets lots of water, maybe a tree (fruit?) to help with erosion? Or all three

Thanks for the ideas! Berries sound interesting. I am thinking about gooseberries, I don't know why. Just curious about them. What do they taste like? Are there any good-tasting cultivars without spines??

The ferrocement is neat! Cool link.

If thistles are doing well, artichokes probably will too.  Not exactly a large bush, but they could be one part of a polyculture you devise that can outcompete your weeds.

I was wondering about that. There are two different kinds of thistles there, both doing well.

Certain varieties of blueberries love bogs and the shores of lakes.  I would suspect that most blueberries will tolerate wet feet, but I can't back that up. 

Ran across this:
http://forums.gardenweb.com/forums/load/permacult/msg0403432314827.html