Earlier US Texas

In 1803 the US bought the Louisiana Territory from France, no sooner was the Ink dry on the Treaty than the US started trying to buy Texas from Spain.
Spain wasn't interested at the time, but following the Mexican Deceleration of Independence in 1811, several Expeditions from Louisiana, attempted to take the Territory.
This semi official Filibustering expeditions ended in 1819 with the US recognition Spanish claims to Texas. this was done in the
The Adams-Onis Treaty

Also called the Transcontinental Treaty of 1819, the Adams-Onis Treaty was one of the critical events that defined the U.S.-Mexico border. The border between the then-Spanish lands and American territory was a source of heated international debate. In Europe, Spain was in the midst of serious internal problems and its colonies out west were on the brink of revolution.

Facing the grim fact that he must negotiate with the United States or possibly lose Florida without any compensation, Spanish foreign minister Onis signed a treaty with Secretary of State John Quincy Adams. Similar to the Louisiana Purchase statutes, the United States agreed to pay its citizens’ claims against Spain up to $5 Million. The treaty drew a definite border between Spanish land and the Louisiana Territory.

In the provisions, the United States ceded to Spain its claims to Texas west of the Sabine River. Spain retained possession not only of Texas, but also California and the vast region of New Mexico. At the time, these two territories included all of present-day California and New Mexico along with modern Nevada, Utah, Arizona and sections of Wyoming and Colorado.

The treaty -- which was not ratified by the United States and the new republic of Mexico until 1831 -- also mandated that Spain relinquish its claims to the country of Oregon north of the 42 degrees parallel (the northern border of California). Later, in 1824, Russia would also abandon its claim to Oregon south of 54’40,’ (the southern border of Alaska.)
Adams tried to get Texas, but Spain refused, But WI
In 1819 while Negotiations were ongoing- Word was received in Madrid, about a major defeat of Spanish troops in northern Mexico by a Filibustering Expedition from Louisiana.
Officially the Filibusters are there in support of Mexico, But..............
In this Treaty the Border is not the Sabine, but the Nueces to the 100o longitude [eastern N/S border of the OTL Texas top hat] then [OTL] north to the 42o Latitude then West to the South sea

Alt AO Treaty.png
 
Interesting idea, it would butterfly away the Alamo and Texican Independence. California would probably end up being seized by US because of the gold. Its possible that the Neuces River would remain the US-Mexico border in the east, the west would be determined by whatever means the US acquires California.
 
Would the US take all of California, or only the North? I don't know whether there are interesting things in SoCal - and the gold was in the North.
 
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