It consists of two adjacent facilities: the National Astrophysical Observatory of Tonantzintla (Spanish: Observatorio Astrofísico Nacional de Tonantzintla - OANTON), operated by the National Institute of Astrophysics, Optics and Electronics (INAOE), and the National Astronomical Observatory - Tonantzintla (Spanish: Observatorio Astronómico Nacional - Tonantzintla—OAN - Tonantzintla), operated by the National Autonomous University of Mexico (UNAM).

OAN - Tonantzintla is located immediately to the east on mostly unused property.

[1] OANTON was dedicated in February 1942 in a ceremony attended by the President of Mexico, Manuel Ávila Camacho, and other dignitaries.

[2] The project was begun some time earlier by Luis Enrique Erro, who was an astronomer by training but for many years had been the Mexican ambassador to the United States.

[8] OAN began looking for a new location 1966, and determined that Sierra de San Pedro Mártir would be an excellent site.