The Simi Hills were home of the Rocketdyne Santa Susana Field Laboratory ( SSFL ) for open-air testing of rocket engines from 1947 to 1990 , and the site of experimental nuclear reactor experiments with four nuclear accidents between 1959 and 1969 ; these projects and accidents were declassified in 1989 . The first accident , in 1959 , was the most serious with a full meltdown . The extent of the accident is unknown due to instrument limitations , other than it is released extensive radiation . More radiation was released in the 1959 event than in the Three Mile Island accident 20 years later . The groundwater under portions of the Simi Hills , contaminated with toxins and radionuclides that were also historically used at SSFL , has been and are a key concern in new development decisions and the SSFL property 's future limited to parkland use after an impending cleanup , initiating preservation of more open space in the range
Three Mile Island accident
Three Mile Island accident
Simi Hills