The Killing Fields...

"...were a number of sites in Cambodia where large numbers of people were killed and buried by the Khmer Rouge regime, during its rule of the country from 1975 to 1979, immediately after the end of the Vietnam War.
At least 200,000 people were executed by the Khmer Rouge. Analysis of 309 mass grave sites by the DC-Cam Mapping Program and Yale University indicate at least 1,386,734 victims. Estimates of the total number of deaths resulting from Khmer Rouge policies, including disease and starvation, range from 1.4 to 2.2 million out of a population of around 7 million. In 1979, communist Vietnam invaded Democratic Kampuchea and toppled the Khmer Rouge regime."

"The best known monument of the Killing Fields is Choeung Ek. Today, it is the site of a Buddhist memorial to the terror. The memorial park has been constructed around the mass graves of many thousands of victims in Choeung Ek. The utmost respect is given to the victims of the massacres through signs and tribute sections throughout the park. Many dozens of mass graves are visible above ground, several which have not been excavated as of yet. Commonly, bones and clothing surface after heavy rainfalls due to the extremely large number of bodies still buried in the area. It is not uncommon to run across the bones or teeth of the victims scattered on the surface as you tour the memorial park. If these are found, you are asked to notify a memorial park officer or guide."

Text in: http://en.wikipedia.org/wiki/The_Killing_Fields