They can't support pasture on that land, it's too arid. This land was affordable to them because it's extremely marginal, not suitable for farming or ranching. Additionally, the loss of native plants from overgrazing has caused their thin layer of topsoil to desiccate and blow away as dust. There's nothing on the landscape to recycle the manure into new grass - no rain to wash it away or support fungi, no insects to break it apart and bury it, and no plants left to recycle the nutrients. Anything that does sprout gets immediately ripped out or trampled by hungry, overcrowded animals.
To give you an idea of how arid it is, the blue pin in the center of the picture is the Tranch properly. It's in located in an area where nothing besides scrub is able to grow.
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It was a folly to try ranching here from the get go. There's a property north of them with access to a creek and another to the east with a small pond, so they might be able to grow.... anything, but not the Tranch property.