I visited the McDonald Observatory which is located outside of Fort Davis, TX up in the mountains. They have multiple telescopes and offer a self guided tour which is what I did. The observatory is a research arm of the University of Texas at Austin Astronomy Program.
It is 10 meters across but uses a different design than the other telescopes. The signs said that this new design may become the standard for future telescopes as it is more effective than conventional telescopes. They were in the process of making some changes to it for some dark energy research so the face of the array was turned away from the viewing area.
To learn more about the observatory you can checkout mcdonaldobservatory.org.