Due to the outbreak of the Reform War in Mexico between conservatives and liberals (1858-1860), the rebel Ignacio Pesqueira invited the U.S. politician Henry A. Crabb to colonize the northern frontier region in the state of Sonora.

Crabb's men took up positions inside an adobe building but it was later set on fire by an O'odham warrior, forcing their surrender.

George Cardwell, an associate of some of the expedition's members, wrote that at the conclusion of the battle, 25 U.S. citizens had been killed and the remaining 58 were separated into groups of ten and executed by firing squad.

[citation needed] The Mexican commander, Hilario Gabilondo, who had received instructions from Pesqueira to shoot the prisoners, refused to carry out his orders and left with a fourteen-year-old American boy named Evans.

[citation needed] General Crabb was allowed to write a letter to his wife before being executed by a firing squad of 100 men.

Cardwell himself wrote that "Mr. Crabb left here about January last, ostensibly for the purpose of mining in the Gadsden purchase, and settling there; but really intending to conquer Sonora, and in process of time add it to the slave states.

Cardwell writes that "some days" after the Caborca affair, a group of 20 Mexicans crossed the border, from San Juan, into Arizona and captured four men of Crabb's party who were resting in a general store due to illness.

A squad of sixteen other recruits was not so fortunate, and after crossing the border were intercepted by the same 200 men who had encountered Major Wood and Captain Oury.

These men (among whom was Freeman McKinney, the San Jose law partner of the notorious Parker H. French) surrendered without a fight, but were executed like the others.

In California and New Mexico Territory, news of the massacre created a clamor for revenge against the Mexicans but the incident was eventually put aside and forgotten.