[balrog666]

I note that 17,500 years ago was during the last ice age -- ocean levels would have been lower, so if there was a low ridgeline along that route, it might have allowed people to move on foot between the two areas. No need for a manmade bridge then, and it would explain how a sandbar might occur naturally

That sounds like a better explanantion.

[colorado tanker]

Ocean levels have risen a lot, even in the last 5,000 years.