April 25, 1846

Thornton Affair

Thornton Affair: Mexican forces capture a U.S. dragoon patrol

Thornton's dragoons rode in through the only opening in a wall of chaparral, and found Mexican troops closing the exit behind them.

25 April 1846, at Rancho de Carricitos

On 25 April 1846, Captain Seth Thornton led 63 U.S. dragoons toward Rancho de Carricitos, about 28 miles upriver from Fort Texas, to investigate reports that a large Mexican force had crossed the Rio Grande.

Mexican general Anastasio Torrejón was moving nearly 1,600 cavalry and infantry toward the same ranch. He surrounded Thornton's men inside a field enclosed by dense chaparral.

Trapped inside the field

Gunfire stopped the dragoons' attempted charge, and Mexican troops blocked escape through the brush. The survivors surrendered.

The National Park Service account gives 11 U.S. dead and 46 prisoners, Thornton among them; casualty totals differ between official and later accounts.

Word reached Fort Texas later the same day, and General Zachary Taylor forwarded the news that hostilities had commenced.

Whose soil it was

The site lay north of the Rio Grande but inside the disputed Nueces–Rio Grande strip, where sovereignty was unresolved. Polk's later assertion that American blood had been shed on American soil was therefore a contested political claim.

Congress had not declared war, and Palo Alto and Resaca de la Palma would be fought on 8 and 9 May before it did.

The exact spot is now lost: the Rio Grande has repeatedly shifted its channel, and the nineteenth-century distances followed a winding route.

Sources

Researched 23 Aug 2026 6 sources 2 audit passes

How this was checked

Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →

What the sources leave uncertain

The date and basic sequence are firmly documented.
The exact ranch location has been lost because the Rio Grande changed course and nineteenth-century distance measurements followed a winding route.
Casualty totals vary in official and later accounts. The current National Park Service Carricitos account gives 11 dead and 46 captured; a National Archives teaching account gives a different breakdown.
The site was north of the Rio Grande but within the disputed Nueces–Rio Grande strip. Its physical location does not validate Polk’s later assertion that it was uncontested U.S. soil.