Comment Snake River? (Score 1) 678
Sometime back in my Geomorphology class back in the early 1980's I either read of the professor said there was a theory the Snake River wound its way down the backside of the Sierra Mountains and down to Baja and joined up with the Colorado River. The change came after one of those massive Northwestern volcanic eruptions. So it doesn't seem so far fetched.
So by that reckoning, any pipe doesn't have to be built the whole way. Just over that portion where it got shunted to the Columbia River back to its old course.
At late middle age, my memory could be faulty also. Or the theory may have been disproven by now.