Description

Agua Fria River water wheel, Yavapai County, Arizona Territory, c. 1890's. 

Photograph of a man, with his horses and dog, pointing at a small outflow cascade of water from the Agua Fria River. A mining water wheel and mill is behind him. 

Separating valuable metal from the waste rock was seldom an easy task. The earliest, simplest and most affordable method of crushing ore was with the use of an arrastra. Arrastras (also “rastra” or “arastra”) had their origins in Mexico. They were the earliest type and used during the California Gold Rush in the 1850s. These devices consisted of a flat track of stone inside a low wall of rock or wood, a retaining basin to capture and hold the ore, and a center post and horizontal shaft made of wood or from small tree trunks. The ease by which they were built and operated made them ideally suited to small mining operations. Powered by horse or mule, the shaft would drag one or more large stones in a circular path on top of the flat stone base, crushing the ore that has been placed in the basin. When water was plentiful, flumes and water wheels were often used instead of animal power.

More elaborate arrastra mills were often housed in a building and powered by water from flumes or even steam power. As mining technology evolved, arrastras and water wheels were replaced by much larger and more effective milling methods and machinery. Stamp mills became the best way to crush and process bulk rock at most mines when adequate capital was available.