Researchers have identified shocked quartz at three key archaeological sites from the Clovis period: Murray Springs in Arizona, Blackwater Draw in New Mexico, and Arlington Canyon in California's Channel Islands.[5] Shocked quartz represents sand grains physically altered by extreme heat and pressure.[5] Mammoth bones with cut marks just below the Younger Dryas boundary and preserved footprints were found at the Murray Springs site.[3] At Blackwater Draw, Clovis culture artifacts and slaughtered animal bones end abruptly at the Younger Dryas boundary.[3] At Arlington Canyon, human remains and pygmy mammoth bones disappear just before this boundary, followed by several centuries without archaeological finds.[3] The radiocarbon dates from these sites are very close, confirming the almost simultaneous occurrence of the changes despite their distance.[3]