The McDonald Observatory is an astronomical observatory at an elevation of 2.070m (6,790ft) above the sea level, in Mount Locke, in Texas, United States.
The road to the summit is asphalted. It has steep grades. It’s called Texas State Highway Spur 78 or Spur 78. The road is 1.5 miles (2.4 km) long and is located within Jeff Davis County. The observatory was built in 1932. It’s one of the world's leading centers for astronomical research, teaching, and public education and outreach. At its terminus at the summit of Mt. Locke, Spur 78 has the distinction of having the highest elevation at any point on the state highway system.