Video from 2014. Canadian Museum of Nature.
"A French farmer kept quiet for years after stumbling across the skull of an extinct ancestor of the elephant near the Pyrenees mountains, the Natural History Museum of Toulouse has told AFP." Source: Archaeology News Network.
Note: According to Live Science (2016), "Mastodons went extinct around 10,000 years ago. There are many theories as to why. Most of these theories boil down to climate change and/or human hunting, according to Simon Fraser University. Some scientists think that the Earth warmed up from the Ice Age too quickly for the mastodon to adapt or that humans hunted them to extinction." It's also possible that they were wiped out by disease.
Climate change and disease sound like the most probable causes. The idea that small bands of prehistoric hunter-gatherers could have hunted the mastodon to extinction doesn't seem very likely at all.
Related: 10 Important Facts About Mastodons