New Scientist, March 27, 2004, page 16:

A study of mammoth tooth enamel and three Clovis sites (10-13K years old) show a wide variety of isotope ratios, which basically means that the large numbers of mammoth bones at each site accumulated over thousands of years. They were not all slaughtered en masse.

At another site, where all the mammoths drowned at once, the isotopes were the same. One wonders if these mammoths that drowned at once was during a global cataclysm....