[uglybiker]

Okay. I must have my Ice Age lakes mixed up. I thought lake Agassiz flooded the Columbia River basin into the Pacific.

Which one was that?

[SunkenCiv]

One idea is, as the edge of the icecap receded north, instead of running off into the Mississippi River, it ran into the newly uncovered St Lawrence.

[Lucius Cornelius Sulla]

Which one was that?

You are thinking of Lake Bonneville, the ancestor of the Great Salt Lake, formed about 30,000 BC from glacial runoff, drained into the Columbia River through Idaho around 124,000, probably due to continued glacial melting.