Mount Diablo has long served as a guide and landmark to people far below, making it a natural site for radio and transmission towers. As early as 1928, the Standard Oil Company and the U.S. Dept. of Commerce jointly built a 75-foot-tall aviation beacon for commercial aviation that was visible for 100 miles. The beacon produced a light equivalent to 10 million candles and was later transferred to the Summit Building, where it remains. Special services antennae received and relayed police, fire, and other emergency civil defense messages. As technologies changed and the need for such towers diminished, Mount Diablo State Park set a long-term goal of removing all towers from the summit.