The “arrastra” was the earliest known means of crushing ore and was used by the early prospectors. The word “arrastra” is of Spanish origin and is described in the Britannica Dictionary as a crude Spanish- American ore-crushing mill with vat and rollers worked by a horizontal beam. This particular arrastra was moved to its present site from the Moose Mine on Mount Bross in the early 1970’s.
It is constructed of two large rocks. The bottom rock hollowed out became part of the stream bed. The top rock is attached to a horizontal pole that could be turned in a circle. Depending on the size of the arrastra, man, ox, or burro was used to turn the stone. As the gravel from the stream bed was washed over the bottom rock the top rock was dragged in a circle, crushing the ore into a fine mixture. The running water would wash the lighter particles of stone and debris downstream, leaving the heavier gold bearing particles to settle on the bottom of the hollowed out base.
Today, one of these early arrastras is still in place in Buckskin Gulch, three miles upstream from Alma. The base is deeply worn from hours of grinding during the Gold Rush Days.