Soldiers, settlers, and laborers, part of two mission colonies under the administration of Francisco Garces, mined placer gold in the southeastern Chocolate Mountains in 1780 and 1781. Their mining methods were simple. Placer gold was recovered by winnowing (tossing the lighter materials away by gently shaking a blanket in the wind). Dry washers may also have been used. Their mining endeavors, almost recreational in nature (as they were not mining gold for a living) ended abruptly when the Yuma Indians attacked the two missions on July 17, 1781, killing at least 50 men and taking 67 women and children captive. Mining activity was resumed in this area only after the establishment of the Mexican Republic in 1823.
Also worked in the 1780’s were the placer grounds of Jackson Gulch and the oxided ores of Padre Madre Valley in the Cargo Muchacho Mountains. The Padre y Madre Mine, located 13 miles northwest of Yuma and 3 miles northwest of Ogilby, was one of the most extensively developed early mines. The mine enjoyed a modest production from the 1780’s until 1894 with few interruptions.
Even the name of the mountain range speaks of the early interest in mining in the area. Reportedly in the early 1800s two young lads playing at prospecting in imitation of their fathers came into camp with their shirts loaded with gold ore. Their antics resulted in the name of Cargo Muchacho, for the mountains where they had made their find. Although it is difficult to estimate the area’s gold production during the Spanish and Mexican eras (1780-1848) it was probably not more than half a million dollars.
William P. Blake, a geologist with Lt. Williamson’s Pacific Railroad exploration party, was the first Anglo- American to visit the southern portion of the Cargo Muchacho Mountains with an eye toward mining. In 1853 he reported seeing several quartz veins from three inches to a foot or two in thickness. His observations were recorded in official government reports, but no one acted upon this evidence of possible mineralization until the Southern Pacific Railroad between Yuma and the coast was completed.