Would a more accurate account of North America eventually convince the colonies that a territory from the Pacific to the Atlantic wouldn't be a good idea?
If it isn't obvious, I find that North America is so Balkanizable.
ST
It wasn't obvious what you meant, even when seeing the hidden message.

I suspect that without the development of railways it would probably have splintered due to the differences. However, given the richness of some of the west coast, even before gold was discovered, and the view in the US at the time I don't think more details of the geography would actually stop an initial conquest.
As jycee says you really need a check by another power. Most likely Britain in 1812, with possibly later conflicts coming from this but a Mexico that got it's act together could hold onto California at least and possibly with some clash with Britain resulting from a longer Mexican war Oregon could also be lost. If the US was cut off totally from the west coast this would probably significantly delay the expansion westwards and settlement of the great plains.
Steve