Maybe related or can point you in the right direction. I recently visited an area resort on Cape Cod where a golf course was being renovated. On a tour of the facility I asked why there was so much sand being put down and where the loam or topsil was. They put down atleast 8" of a 80% sand and 20% seed mix...and no loam or soil! Pretty sure it was rolled out. They were planting bent grass (tee boxes, fairways, greens) and bluegrass on the first cut. True they have drainage and irrigation, but I was surprised they were using a mix with primarily sand.

Centipede and St Augustine look much the same. Find a blade that has not been mowed. At the tip centipede will be pointed while St Augustine will have a boat tail shape. But it has to be St Aug because centipede only grows in full sun on p-poor soil. Best thing you can do is never let it die. While that may seem obvious, most grasses will go dormant when dry but St Aug goes straight to dead. That does not mean it has to be soaking wet all the time. It just needs to not dry out continuously for several weeks. Proper watering for St Aug is like all lawns. Water it deeply (one inch at a time) and infrequently (this time of year it might be every 14 days). Mulch mow at your mower's highest setting for spectacular turf. It will take several weeks after you fertilize for all the grass to get up to that height but you will thank yourself for doing it. Tall St Aug will go much longer into a drought before it needs water. It will also help keep weeds out. I have a rural lawn surrounded by all kinds of weeds but none are sprouting up in the middle where it is tall. Now I'm working on spreading the grass out to mingle with the weeds and choke them out. If you want it to excel, it really needs fertilizer like yesterday. You'll get the fastest results from using something organic like alfalfa pellets (rabbit chow) once a month at a rate of 20-30 pounds per 1,000 square feet. The reason that is faster than chemical fertilizers is that you can only apply chems once now and again in the fall or you risk burning the grass. Or you could apply both now and continue with the alfalfa for a few months to keep the green going. It will become much more dense, also. Now for some pictures to illustrate what I'm talking about. 1. Tall St Augustine in a lawn setting. This is mowed at the mower's highest setting. Fertilizer is corn gluten meal. 2. St Augustine that has not been mowed since last October. Pic was taken on Valentines Day when all the rest of the lawns were dormant but this one was not. Dog is 35 pounds so not a puppy. This is an experiment I'm doing with my rural lawn. Note there are no weeds in sight. 3. Effect of alfalfa pellets on zoysia lawn. This lawn is just like yours (thin). The spot was fertilized in May 2011 and photo taken in June. Note the improved density, color, and growth.

hoovb is right. 90% chance it is Marathon dwarf fescue. It could be Marathon, Marathon II, or Marathon III. They get dwarfier with higher numbers. Now, having said that, fescue is now and forever was, the wrong grass for the inland areas of SoCal. For me, inland means anywhere east of the 405 freeway or I-5 or the coastal range of mountains/foothills (whichever is closer to the beach). You are on the wrong side of I-5 and the coastal range. What you should have is either bermuda or St Augustine. Both of those are heat loving plants. Fescue is a cool weather grass which has been made to work only with daily watering. With either bermuda or St Aug you can get back to weekly watering even in the summer's hottest heat. With your drought you should be thinking of alternatives to fescue. Now about this crabgrass you say you have...do you get seed heads every week or two? Are the blades pointy before you mow or are they more rounded? I'm asking because St Aug is often mistaken for crabgrass because they are both coarse bladed varieties of grass. St Aug has the rounded tips and no seed heads (very rare). All other grasses have pointy tips. If what you have is St Augustine and you are willing to go and grow that, then you don't have to do much of anything and it will take over. St Aug will dominate every other grassy plant with proper care (mulch mow at mower's highest setting, water once a week in the heat and much less often in the cool months, and fertilize 3x per year). If you would like to change to bermuda, you can get bermuda seed very cheap or you can get bermuda sod. The sod is a much MUCH better variety of grass and should never be mixed with the seeded varieties. Seeded bermuda is the grass people complain about. Sodded bermuda is the grass everyone wishes they had. In SoCal they use sodded bermuda for golf greens. Bermuda takes a lot more care than St Aug if you want it to look nice, but it has the advantage of not dying when it goes completely without water for several months.

I am with Laceyvail - don't use weedcloth in a garden! If you google weedcloth on many of the forums, you'll see lots of opinions that agree with this. Roots of woody plants from below and weed seeds that have blown in from above will root into the fabric and you will come to regret putting it in. It keeps mulch separated from the soil, so the soil doesn't get new organic matter and as the mulch breaks down and organic matter blows in you have new growing medium on top of the landscape fabric. It's an all around bad idea and the nightmare is when you decide to get rid of it . . . DH did this once many years ago and it both didn't work and was misery to remove a couple of years later. It does have its uses - to keep drainage material from washing out from behind a dry-stacked stone retaining wall, to keep soil in a basket where you want to plant annuals, or under a walkway to separate layers of soil and drainage material, but you will come to regret ever using it where there are plants growing in a garden. Instead of using landscape fabric, I mow down everything to ground level and sometimes will dig a few weeds that I know to be stubborn, put down heavy cardboard and then a heavy layer of medium fine mulch on top of that to a depth that settles to about 3 inches. That's enough to prevent most weeds from sprouting and to keep most of the already present weedy plants from coming up through. I let that sit for a few weeks to a year and then plant. If you are in a hurry to plant, though I can't imagine that this is a great time to plant in most areas of Colorado right now, you can use some type of contact weed killer (they range from gas flame weed torches to strong vinegar to Roundup.) One more quick comment - since you are planning to redo the whole area, now would be a perfect time to add any soil supplements like more organic matter to help hold moisture and nutrients.