The Planchas de Plata

The documented silver find that named Arizona

In 1736 a Yaqui man named Antonio Siraumea found silver on Bernardo de Urrea's Rancho Arizona in what is now Sonora, a few miles south of the modern border. Not silver ore. Native silver, lying in the ground as slabs and lumps, and the accounts are hard to believe until you check them. One mass is recorded at more than a hundred arrobas, which is something over twenty five hundred pounds of metal.

The place was called Planchas de Plata, slabs of silver, and also Bolas de Plata, balls of silver. Word travelled and men came, and it very quickly became a legal problem rather than a mining one.

Juan Bautista de Anza, the Justicia Mayor, arrived that November, named the site San Antonio de Padua, and impounded everything already taken, hauling it to Urrea's ranch. The Spanish crown then made an argument that decided the case: silver lying loose in that form was not a mine but a treasure trove, and treasure belongs to the king. Soldiers cleared the miners off.

Here is the part that outlives the silver. Anza's scribe, Manuel José de Sosa, dated the impounding documents at Arizona, the name of Urrea's ranch. Copies went to Guadalajara and Mexico City, and the whole affair became known as the silver of Arizona. That is where the name of the state comes from. Not from a Spanish phrase about arid zones, which is a folk etymology, but from a ranch in Sonora where somebody dug up a two-thousand-pound lump of native silver.

The district is in Mexico, near Nogales, and it is not a collecting destination. What is worth doing on the US side is Tumacácori and Tubac, where the Park Service tells this story on the ground the Anza expeditions actually crossed.