Dean
Can you use the Colorado along much of its length for transport? I though the Grand Canyon and such were pretty much impassable.
Steve
Er, I'm not sure. I know that today the Grand Canyon is considered impassable, but I'm not sure how much of the Colorado is impassable naturally and how much is impassable because of dams and river alterations made in the last century and a half. Parts of it would be for river trade, I'm sure. You actually don't need too much depth for river trading, through; flat bed boats out east only went about 2-4 feet under the water.
However, it wasn't uncommon for western travelers (wagon especially) to move along rivers, since major rivers both provided water and a good sense of direction, both of which are extra valuable in the American South West.