I'd take Sissoos over Mesquite. Sissoos grow extremely fast if you are looking for fast growing trees. I also like Chinese Elm. Not necessarily fast growing, but I like the look. I have all 3 growing and a few others. I have vines growing along my fence - I don't know what the name of it is, but it branches out all over the place and has hundreds of yellow flowers! I also have very leafy, ground covering plant in front of my house that puts out both white and yellow flowers - lot of them! Likes water, though, especially during the summer. I can get the name of it from Whitfill's are interested, though the vines I have no clue, got them at a nursery that was going out of business. I am also experimenting with growing a Queensland Bottle Tree (not to be confused with other Australian type of bottle trees). I was at a house that was in a pond club that was doing a tour of homes with Koi ponds. One of them had a couple of these trees that had grown to 20 plus feet. Absolutely gorgeous and extremely different than most anything else you find around here and it loves Phoenix weather. If interested, there is a seller on Ebay that I bought mine from. They aren't exactly fast growing, but it's a project tree. I'm not a fan of palm trees, just my preference. They grow "wild" on my property and I have to pull them out all over the place. There is another type of desert tree growing on my property that I didn't plant but let grow. I have no idea what the names of those are, either. One of them is 3 years old and about 21 feet tall. Beautiful tree and actually gives some good shade. I saw one at a museum that they had planted a few years back, but I can't remember the name of it. I would also suggest thinking about pine trees. They are ever-so-slow growing but they can take whatever weather this city can give it, unlike my Ficus trees which sustained major damage in the recent extreme frost session we went through. I was lazy though, I could have saved them - wrap C-9 Christmas lights throughout them, especially on the tops if you can get to them and the heat coupled with covering them up does a nice job of helping them weather extreme cold. Yes, I have in the past wrapped C-9 version of Christmas lights around certain plants and trees that are susceptible to extreme cold when the forecast is for hard freeze and yes, it works. May I also suggest a Koi pond? Just for fun. Try starting with a small, preformed shell and see if you like it. Get some Koi and goldfish. They're fun to have! Small ponds don't take a lot of work and the fish learn to know you and the Koi will even come up to you! They survive the heat and the cold. I have one I made out of horse trough and 2 more that are preformed. I haven't delved into the larger type with liners - just haven't got there yet. Whatever you end up doing, have fun with it!

I would just cover it in stone pavers. It will be easier to keep it clean.

Before deciding on groundcover, as Mad Gallica suggested, you want to think about use. Does it get a lot of foot traffic and if so, is it all over or in particular spots? Do you have kids or dogs who will be running or playing in the area? Do you want to have open level spaces for gatherings? Do you want to do more or less maintenance? Some groundcovers look great but either don’t do well with a lot of foot traffic or can be a trip hazard if folks are walking there. Some will spread quickly, but then need a fair amount of maintenance to keep out of paths, but others will spread more slowly and may need mulching and some initial weeding, but won’t be difficult to control once established.

I would check locally on grass varieties and mixes. I put in 1600 square feet of lawn, using a blend that the local sod farm recommends for my zone 9 location. It's a very small lawn, I can mow it in less than 30 minutes with a battery operated mower and it doesn't use that much water. IF you want a place for kids and dogs to play, nothing beats turfgrass. But the concerns voiced here are legitimate, so see what kind of grass is available and exactly how much water you are talking about. Your space is small - less than 1/2 of mine - but it would provide an ample play area and a rest for the eyes. I looked at all of the artificial grass options that i could find before I put in the lawn and they all got hot when in the sun. Turfgrass actually stays cool.