A population of Columbian mammoths that lived between 80,000 and 13,000 years ago on the Channel Islands of California, away from the mainland, evolved to be less than half the size of the mainland Columbian mammoths. They are, therefore, considered to be the distinct species "M. exilis", the pygmy mammoth (or a subspecies, "M. c. exilis"). These mammoths presumably reached the islands by swimming there when sea levels were lower, and decreased in size due to the limited food provided by the islands' small areas. Bones of larger specimens have also been found on the islands, but whether these were stages in the dwarfing process, or later arrivals of Columbian mammoths is unknown.