The 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.