The Sa'ami are generally conceded to have invented "cross country" skis, and probably the other kinds as well.
With 25% of Earth's land surface given over to reindeer and musk ox herding, those bad boys got around. We can't be sure of who was using a ski in Western China at the time, but there's no mystery to how they found out about skis.
What "time"? Do you have conclusive evidence as to when snow and ice either receeded enough to make the land habitable, or increased to make life more difficult?
Goelogical evidence suggests the later.
Reindeer and Musk ox are tundra swamp animals . Not much lumber around there to make ski's. Unless they were 3 foot tall ones. Opps, those trees are 3 feet tall NOW. They were probablt much shorter THEN. If course, something catasrophic could have happened....
I would like to disagree with you but, I've come to respect your knowledge of northern people. We'll let it ride...for now.(Ahem)