Round Top Mountain is a mountain located at the western end of the Sierra Blanca area in Hudspeth County, Texas near the town of Sierra Blanca. The area includes the Finlay Mountains, Triple Hill, and Sierra Blanca quadrangles as well as parts of the Fort Quitman and McNary quadrangles. Round Top Mountain is known for containing deposits of beryllium as well as the largest deposit of heavy rare-earth elements in the United States.