My first post:

I have a hill (about 2 acres) that is mostly bare on the slopes with some scrub type trees. This is subsoil I suppose. The top soil was scraped off back in the 1940's - I still have the topsoil in mounds but trees are growing out of it... it will take some cash to redistribute. Erosion is slow but taking place.
What is the single most important thing I can do right now to save my hill?

You can recover that hill completely by mobbing goats or cattle and walking them over it. If there is nothing growing there, you'll have to provide food and water. Unroll a couple hay bales and bring in a water trough. Keep the animals very close together with dogs, fencing, or people. Move them on as the food is eaten or fouled with dung. If you had 40 or so cattle it should only take a day or two. Yes I know that's a lot of animals for 2 acres. Try to get the same pounds per acre with goats. I don't know what the animal unit conversion is for goats.

An easier approach would be to send soil samples to The Texas Plant and Soil Lab.