From the Austin-American Statesman article, "State’s biggest park offers improved access and more campsites", about TPWD’s Big Bend State Park (not the national park):
"The state acquired the land for this park in 1988. Heavy grazing by sheep and goats from the 1850s to 1940s took a toll, diminishing the grasslands and giving shrubs an opportunity to take root. But it’s not as desolate as it seems. The park is home to three of the four highest waterfalls in the state and about 120 perennial springs."
Read more about Texas’ desert grasslands at the Native Prairies Association of Texas (NPAT) web site.