HI! I saw your question and I thought I'd answer it! <3
The section of Texas that is known for its many lakes, reservoirs, and hills is either, Llano Basin or the North High Plains. I'd be careful if I were you because I don't know if this answer is 100% accurate.
This is just MY personal answer, you don't have to use it if you don't want! <3
-Sincerely BlushP1nk,