Design
An arrastra (sometimes spelled arastra) is an early form of ore mill. Instead of using steam or internal combustion power sources to rapidly mill lots of ore, the arrastra instead used a mill stone mounted to a single post. The mill stone was rotated by a mule or horse (or, rarely for large arrastras, a team of horses). This had the advantage of allowing the small miner in the field to set up his own field, but had the disadvantage of not being terribly efficient.

Comments
Arrastras generally went out of use after the invention of steam engines. Small steam engines could winch themselves to mine sites and then be able to process much more ore in a given time. The internal combustion engine put the final nail in the arrastra's coffin.