The 2,848 acres (1,153 ha) Santa Susana Field Laboratory located in the Simi Hills, was used for the development of pioneering nuclear reactors and rocket engines beginning in 1948.
The site was operated by Atomics International and Rocketdyne (originally both divisions of the North American Aviation company).
The Rocketdyne division developed a variety of liquid rocket engines.
Rocket engine tests were frequently heard in Simi Valley.
The Atomics International division of North American Aviation designed, built and operated the Sodium Reactor Experiment, the first United States nuclear reactor to supply electricity to a public power system.[Also from Wikipedia:  The Boiling Water Reactors (BORAX) experiments were five reactors built between 1953 and 1964 by Argonne National Laboratory.
They proved that the boiling water concept was a feasible design for an electricity-producing nuclear reactor.
One of the BORAX reactors (III) was also the first in the world to power a city (Arco, Idaho) on July 17, 1955.[59][60]  Both claims can not be correct. ]
The last nuclear reactor operated at SSFL in 1980 and the last rocket engine was produced in 2006.
The SSFL has been closed to development and testing.
The site is undergoing investigation and removal of the nuclear facilities and cleanup of the soil and groundwater.
The Boeing Company, the US DOE, and NASA are responsible for the cleanup.

In July 1959, the Sodium Reactor Experiment suffered a serious incident when 13 of the reactor's 43 fuel elements partially melted resulting in the controlled release of radioactive gas to the atmosphere.
The reactor was repaired and returned to operation in September, 1960.
The incident at the Sodium Reactor Experiment has been a source of controversy in the community.
Technical analysis of the incident intended to support a lawsuit against the current landowner (The Boeing Company) asserts the incident caused the much greater release of radioactivity than the accident at Three Mile Island.
Boeing's technical response concludes the monitoring conducted at the time of the incident, shows only the allowable amount of radioactive gasses were released, and a Three Mile Island-scale release was not possible.
 The case was settled, it is reported, with a large payment by Boeing.
In September 2009, The U.S. Department of Energy sponsored a public workshop where three nuclear reactor experts shared their independent analysis of the July, 1959 incident.

The Santa Susana Field Laboratory also hosted the Energy Technology Engineering Center.
The center performed the design, development and testing of liquid metal reactor components for the United States Department of Energy from 1965 until 1998.

The Santa Susana Field Laboratory includes sites identified as historic by the American Institute of Aeronautics and Astronautics and by the American Nuclear Society.
The National Register of Historic Places listed Burro Flats Painted Cave is located within the Santa Susana Field Laboratory, on a portion of the site owned by the U.S. Government.
The drawings within the cave have been termed "the best preserved Indian pictograph in Southern California."
The 2,848 acres (1,153 ha) Santa Susana Field Laboratory located in the Simi Hills, was used for the development of pioneering nuclear reactors and rocket engines beginning in 1948. The site was operated by Atomics International and Rocketdyne (originally both divisions of the North American Aviation company). The Rocketdyne division developed a variety of liquid rocket engines. Rocket engine tests were frequently heard in Simi Valley. The Atomics International division of North American Aviation designed, built and operated the Sodium Reactor Experiment, the first United States nuclear reactor to supply electricity to a public power system.[Also from Wikipedia:  The Boiling Water Reactors (BORAX) experiments were five reactors built between 1953 and 1964 by Argonne National Laboratory. They proved that the boiling water concept was a feasible design for an electricity-producing nuclear reactor. One of the BORAX reactors (III) was also the first in the world to power a city (Arco, Idaho) on July 17, 1955.[59][60]  Both claims can not be correct. ] The last nuclear reactor operated at SSFL in 1980 and the last rocket engine was produced in 2006. The SSFL has been closed to development and testing. The site is undergoing investigation and removal of the nuclear facilities and cleanup of the soil and groundwater. The Boeing Company, the US DOE, and NASA are responsible for the cleanup.
In July 1959, the Sodium Reactor Experiment suffered a serious incident when 13 of the reactor's 43 fuel elements partially melted resulting in the controlled release of radioactive gas to the atmosphere. The reactor was repaired and returned to operation in September, 1960. The incident at the Sodium Reactor Experiment has been a source of controversy in the community. Technical analysis of the incident intended to support a lawsuit against the current landowner (The Boeing Company) asserts the incident caused the much greater release of radioactivity than the accident at Three Mile Island. Boeing's technical response concludes the monitoring conducted at the time of the incident, shows only the allowable amount of radioactive gasses were released, and a Three Mile Island-scale release was not possible.  The case was settled, it is reported, with a large payment by Boeing. In September 2009, The U.S. Department of Energy sponsored a public workshop where three nuclear reactor experts shared their independent analysis of the July, 1959 incident.
The Santa Susana Field Laboratory also hosted the Energy Technology Engineering Center. The center performed the design, development and testing of liquid metal reactor components for the United States Department of Energy from 1965 until 1998.
The Santa Susana Field Laboratory includes sites identified as historic by the American Institute of Aeronautics and Astronautics and by the American Nuclear Society. The National Register of Historic Places listed Burro Flats Painted Cave is located within the Santa Susana Field Laboratory, on a portion of the site owned by the U.S. Government. The drawings within the cave have been termed "the best preserved Indian pictograph in Southern California."
Simi Valley, California