There is this text in wikipedia in y-dna N page: "The apparent dearth of haplogroup N-M231 amongst Native American peoples indicates that it spread after Beringia was submerged (Chiaroni 2009), about 11,000 years ago."
What it actually says, is that:
1. Bering strait submerged ~11 000 years ago.
2. and that y-dna N went to Alaska LONG AFTER Beringia was submerged and NOT 11 000 years ago. Most probably only in last 1000-1500 years with chukchi who traveled to Alaska. I assume y-dna of N in chukchi is quite recent influx, so only after Chukchi received y-dna, they could deliver it across Bering strait.
3. Hardly N even saw any mammoths, even if chinese still have myths of unicorn and that might be Elasmotherium - real animal, that grazed with mammoths, but most probably they just dig up those as dead animals. N most probably entered in Siberia, only when it was possible to enter it, as glaciers who blocked path to Siberia melted away. If you watch GoT, imagine, that on the side of Amur river starting from Baikal lake there was ice wall and it was inaccessible for NO and anyone else. Eastern side of sea was blocked by glaciers that entered ocean and produced icebergs and the only place that had gates to Siberia was in west around the place, where Yenisei River starts(Baikal lake) and it still have remnants of Q in Asia which were represented with modern Ket people(which also might have linguistical similarities with Dene - at least there is theory, that they have linguistical links), so it was blocked by Q on north side and R nomads in south side. And according to migration paths of N - Uralic migrated into Urals more westernly of Ket.