Maybe there's not very easy access to stuff for mulch, but I imagine a thick layer of organic matter like grass clippings, leaves, chipped trees, weeds, spoiled hay, would make a huge difference. Be warned though, there's some very nasty herbicides out there that can have negative effects for a very long time.
I know Texas juniper is supposed to have allelopatic issues, but I wouldn't worry. If you've got plenty, and access to a chipper, there's your mulch!
I've heard of people using juniper IN their hugelbeds. Cut the juniper, chip it, mulch it, hugel it...
Please note, I'm in New Zealand and have never met a Texan juniper, so I apologise if it can't be used for some reason.

Acording to this article there should be no problem using the cedar.

Here is a link that might be useful: The Myth of Allelopathic Wood Chips

A warm soil certainly stimulates the Soil Food Web so they digest the soil organic matter faster, which is why in the more temperate regions keeping sufficient levels of organic matter in the soil is harder then it is further north where we have 5 months of cold.
Look around to see what types of organic matter are fairly readily available, preferably at low cost. Do your neighbors throw out material that you can use? Do farmers have spoiled hay that you can get? Do you have means of transporting those materials? Do you compost your vegetable waste?

Thanks for the reference on "Allelopathic Wood Chips".

>Do farmers have spoiled hay that you can get?

We have had a drought here. Finding any hay is difficult.

Mytrees - What grows naturally there? Concentrate on native plants for landscaping and you will have fewer problems. Mulching and adding organic matter will help hold moisture.

For vegetable beds, spread soil sulfur granules to lower the pH AND as much organic matter as possible onto the beds - dry leaves, wood chips, coffee grounds, kitchen trimmings, etc.

It's better to amend one area well than to skimpily do the whole garden.

It's tough to find organic matter in hot dry places. I lived in NM for awhile and it's a whole different ballgame from the Midwest.

Got a Starbucks or other coffee shop nearby? Consider picking up coffee grounds by the bagful.

Juice bars or vegetarian restaurants are another possibility. I had a juice bar that would give me a dozen Rubbermaid tubs of rich veggie waste every week if I wanted them.

I live in NM and have quite a bit of juniper on my land. Plants seem to have no problems growing around it. There are even big shrups growing up in the junipers. I harvest some of the needles (a little here, a little there) for mulching beds.

It of course will be helpful to amend the soil with whatever you can find, compost, coffee grounds, kitchen scraps that you have buried, etc. You can try growing green manures that you incorporate into the soil or use as a mulch. Having an adequate mulch is probably going to be the most essential element though. One thing we do is take dead cholla cactus and smash it (it is free). Of course, another option could be burying kitchen scraps, etc, wetting the soil and putting cardboard on top as a mulch. This is not very attractive but it will get the process started. You could also apply conventional mulches on top of the cardboard for a more conventional look.

As said above, the sun is not 'destroying' the organic matter in the soil. Warm climates decompose soil organic matter faster than cool climates. And, dry climates tend to have less soil organic matter because they grow less plant material which is the source of the soil organic matter. Although 30" average rainfall is not all that dry, that's nearly what Seattle gets after all. So shading the soil is not going to help.

Soil organic matter is always transient. It is 'eaten' by the soil microbes to provide nutrients to your plants. You have to keep replenishing it, just as you have to keep eating more food over and over, every day. In my cool short summer climate, once a year can be enough, but in your warmer long summer climate you may have to add organic matter twice a year or more.

You could garden primarily with native plants, Texas has a huge selection of very nice native plants, that's what got Ladybird Johnson inspired after all. They would not need any soil amendments or fancy handling.

But if you're trying to grow conventional veggies and fruit trees and such you may need to do something else. I have grown those in California's extremely basic adobe clay, with less than half the rainfall you get, very successfully. I never amended the soil for the trees. where lack of drainage was an issue I planted them on raised mounds. In summers I built watering moats around them - we got no rain at all in summer. They got mulched every year with compost. Veggies went into clay soil amended yearly with compost and sulfur.

Can you get tree chips from a local arborist? They're usually free for the asking but you have to be able to take a full truck load, usually 5 yards or so, at a time. Tree chips are great mulch and might work for your hugulkultur also.

Goat manure! Texas produces over half of the meat goats in the U.S.. That goes along with a lot of manure. It might even be a local commodity with a more or less set price for a quantity of it - free would be nice but clean (without a lot of bedding) goat manure is worth paying a bit for.

Lowering the ph would have to be handled separately and will probably be a battle over time. Check locally to see what others do or what crop varieties work well.
Best of luck!.

The junipers would work fine for mulch on top if they were ground. Although not toxic for plants I doubt they would do you any good for Hugelkultur. The problem is they do not decompose fast enough. I do not know much about Hugelkultur but from what I have read it is the half way decomposed wood that holds the water. I have cedar in the ground that has been there for over 30 years (fence posts).
I have the same pH alkaline clay soil. Not only in my flowerbeds but also many acres of pasture. You can change the pH in small localized areas but it is really feudal to try and convert large amounts. The suggestions above using plants that accept these conditions are your best bet. Doing this and adding compost and mulch year after year will reward you for your efforts. While getting this going I would suggest a drip system irrigation system and zone your plants as to water requirements.
Also I have found that building the beds above the existing soil/clay works best. Clay soils do not drain well. When putting in new plants it is easy to drown them with over watering if you dig into the existing clays. By building the bed above the existing clays you are providing media for the microorganisms and worms that already exist in the clay. Over time the underlying clays will improve naturally. If the clay is also part limestone then the plant roots will find their way into the cracks and actually expand them for even better root growth.
A wind break also helps slowing down the 100 degree plus, hair dryer, moisture sucking winds from the south in summer.
On a side note you absolutely must plant some Texas Mountain Laurel where the prevailing breeze will bring the fragrance to you in the spring.

Getting your soil test was a great start. Did it include numbers for either CEC or TEC (Cation Exchange Capacity or Total Exchange Capacity)? How about "base saturation" numbers for the primary macronutrients? This information will guide you in balancing your soil so that you have the best opportunity to build organic matter. From a chemical standpoint, calcium promotes a free draining soil. Magnesium will serve to "tighten" the soil to some extent, which would help retain moisture. So, if your C/Mg ratio is skewed, correcting that would be your first step in "fixing" your soil.

If you have only a relatively small area to cover, I'd recommend using pine or fir bark--even if you have to buy it bagged from one of the big box stores. These have a different chemical constituent than hardwood bark and breakdown very slowly, but provide an excellent source of OM over time. Using either hardwood or softwood (i.e. heartwood as opposed to bark) would not be advisable. Without a biologically active soil, it will take forever to breakdown.

If you have a very large area to treat, planting a cover crop would be a great way to proceed. I don't know what the preferred CCs are for Texas, but I'm sure your Extension agent could counsel you on that. In my experience, cover crops can build organic matter very quickly. Here in the north I use hairy vetch and winter rye for my veggie beds and oats for other areas, where I can't till it in. Oats will winter kill here, which is handy. That wouldn't apply in Texas, so again, check with the locals for recommendations.

Someone from the DFW area was offering free horse manure in an earlier thread...

Free Horse Manure from a horse farm. These horses are fed only the very best and the manure is full of nutrients. We will be happy to load for you. The horse farm is very close to Ft.Worth, TX, and not far from anywhere in the DFW metroplex.
Please Call: 817-372-0047

Mytrees, we have the same exact challenge here in San Antonio (at least the part where I live)- high ph sun baked clay soil. It astonished me when I first dumped truckloads of manure and straw bedding on top of raised veggie beds only to find by summer's end that it was like there was little evidence of anything but baked clay! You simply have to dump copious amounts of OM to convert your soil eventually. Not only that, but as you probably already know, here in the sun baked south you need a good 3-4" of mulch on vegetable beds and most trees to retain moisture and block the intense sun from baking the soil. It is just hard to imagine unless you live here just how fast even mulch is broken down. For example, I have to reapply mulch at least once in a single growing season around my veggies, or the sun just gets in there and bakes. Just an FYI- cedar mulch is an A plus mulch so if you have cedar trees in the way feel free to grind them up. In the yard we use a mulching mower to recycle OM back into the lawn, leaves and all.