A Different Mexican Cession

What if, in the Treaty of Guadalupe Hidalgo the annexed land from Mexico was all land north, east, and west of the Colorado and Rio Grande rivers? The US loses most of what's now Arizona, half of New Mexico, south-east Utah, and south-west Colorado, but gains Baja California and a almost-fully natural border with Mexico. How would this change anything?
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This map is North America, right after the treaty in 1848. I tried my best with the river boundaries without tracing anything. Also, I'm too lazy to make Canada historically accurate.
 
Besides giving the US the Baja peninsula, thus making California larger and more likely to be split into two states...no.

The most likely end result is a larger Gadsden Purchase. Or perhaps the US gets tired of cross-border raids by the various Apache tribes and uses them as a reason to occupy northern Mexico. Furthermore the uS was really big on acquiring "transit rights" across portions of Mexico. Given the geography this treaty creates OTL nagging will become a full blown fetish, and the US will be forced to occupy New Mexico to "restore order and ensure the safe transit of commerce and people." Either way I don't see Mexico holding the land much past 1856. Sure it might make the slave state / free state debate a bit different it won't change the inevitable.

Your proposed border is actually very unlikely. Far more likely is a straight line border running from Texas to the Gulf of California, thus including Baja. Nearly all the proposed borders used straight lines and ignored the rivers, except of course the Rio Grande which was a special case because of the Texan War for Independence.

Ben
 
I can't envision a situation in which they'd give up Baja but actually be able to hang on to ~Arizona. It's just not all that plausible.

And if this happens, Gadsden and co. will just buy it (and more) from Mexico, like they originally wanted.
 
Strikes me as being an awful deal. Baja California, AFAICS, is far less valuable than the other territory.

Plus, the borders look worse.
 
A better border, more in tune with plausibility, while also keeping with natural borders, would be one along the from the Rio Grande, then to the Rio Conchos, and then to the Rio Yaqui. I don't have the time to transfer it to a map just now though.
 
I used that border for my Republic of Texas. Other than forcing western immigration (and eventually a railroad) through the Rockies that could cause an earlier development of Colorado; There is really no benefit to that border other than a strangely shaped Mexico. The idea is totally ASB and that territory would just end up being purchased by Gadsden. I agree with you thought that nothing says "natural border" like the Grande Canyon!
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