Congratulations on your new home!* I understand your desire to rescue plants, but most states require you get WRITTEN permission from the landowner before you rescue any plants. Some even require a permit as well, even on private land. * I will admit I have done this myself, but I could have been arrested.* In my case these were not native plants and I was driving past a construction site where the bulldozers were already doing 'their thing'.* There were several neglected roses and some daffodils in bloom.* I asked the foreman of the crew if I could dig up some things and he said yes, but I still took a risk.* If anyone sees you doing this there could be problems without getting written permission and possibly permits.
You may want to contact the Native Plant Society of Texas for help with id of native plants.* There's a chapter in San Antonio.* They might even be willing to help with a rescue of plants.* You will have to make it clear that there are certain plants you want to keep for yourself.* They will probably know all about permits.
Here's how to transplant cactus.* Younger plants will transplant better.* Be sure to mark the south facing side of each cactus and face them in the same aspect in which they grew when you plant them.* In other words, the south facing side of the plant where it has been growing should be south facing when you replant it in your garden.* This is very important.* For cactus you may need some type of large tweezers to handle the smaller plants.* You can even use tongs from your kitchen, but I would recommend padding them so you don't pierce the outer skin of the cactus. Here's some helpful sites.
Several pages to read here.
You can search for native cactus and hopefully id other native plants that could be rescued here.
The Native Plant Project is for the lower Rio Grande Valley, but might be a good resource for you as I'm sure the plants don't realize there is a county boundary line.* They have some wonderful booklets for id.* Here's their main page.
Here's their handbooks which you can view online for free.
Many Yucca have a very deep taproot, most especially the tree forms. Try and transplant the younger plants as you will have greater success that way.* It would be best if you could id which species you will be digging so you can learn about them before you dig.* Here's the Texas native plants database for Trees where you can look up some native Yuccas.
This USDA plants database lists native Yuccas and where they are found.* I find it isn't always accurate and many plants often grow where they aren't indicated here.
Here's Texas native shrubs. You can also click on 'Search' on the left and search for cactus.* I got 3 of the shrub forms when I searched.
Yucca alata - one of the tree species, is one of the most difficult ones to transplant due to a long taproot.
Yucca rostrata, also a tree species, is more forgiving, but I doubt you'll find it where you are located.
This might be helpful to id some native yuccas and other plants.
I can't stress enough that you need to get written permission from the landowner for your own protection.* Good luck with this project.* I'd love to know how it all turns out.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.