McKinley Rocket Base was an American installation utilized and maintained by NASA for the purpose of launching payloads into orbit. Located ten miles south of Highway 949, it was the site of the launch of a nuclear warhead platform in 1968.
In that year, Gary Seven, a human raised by aliens, infiltrated McKinley Base and attempted to sabotage the rocket carrying the platform, in an attempt to frighten the governments of Earth into abandoning their plans to deliver nuclear weapons in orbit. Believing Seven to be a hostile alien, Captain James T. Kirk and Lieutenant Commander Spock of the USS Enterprise, which had traveled back in time from the year 2268, followed Seven to the base in an attempt to stop him, but were subsequently discovered and taken into custody by base security. (TOS: "Assignment: Earth")
"McKinley Rocket Base" was actually a fusion of NASA stock footage taken at the Kennedy Space Center at Cape Canaveral, Florida, and newly-shot scenes at Paramount Pictures studios, namely, the Marlene Dietrich Building across from the Commissary. (Star Trek Encyclopedia 2nd ed., p. 294; wbm)