have they been extinct?
Yes, it became extinct during the late Pleistocene and early Holocene.
Columbian mammoth
Columbian and woolly mammoths both disappeared during the late Pleistocene and early Holocene, alongside most of the Pleistocene megafauna. 
where could you find columbian mammoth? North America to Costa Rica who described it? Naturalist Hugh Falconer
wiki:12737582
Columbian mammoth [SEP] Extinction
Columbian and woolly mammoths both disappeared during the late Pleistocene and early Holocene, alongside most of the Pleistocene megafauna. The most recent Columbian mammoth remains have been dated around 10,900 years ago. This extinction formed part of the Quaternary extinction event, which began 40,000 years ago and peaked between 14,000 and 11,500 years ago. Scientists do not know whether these extinctions happened abruptly or were drawn out. During this period, 40 mammal species disappeared from North America, almost all of which weighed over ; the extinction of the mammoths cannot be explained in isolation. Scientists are divided over whether climate change, hunting, or a combination of the two, drove the extinction of the Columbian mammoths.