GGG Ping.
At some point, the hunters were incented to try to cross a risky land bridge, in search of new stocks/hunting grounds.
They found themselves in Alaska, where the mammoths were abundant, and expansion/settlement would have followed quickly, as well as the extermination of the mammoths in North America.
Iron?
Hmmmmmmmmmmnnnnn. Wonder if they found a meteorite remnant?