Copper mining is one of modern man's most aggressive landscape modifying activities. Whereas early (pre-1900) copper mining was usually labor intensive and confined to relatively small areas in direct proximity to rich ore bodies, the twentieth century has seen greater reliance on large-scale earth moving and more sophisticated ore-processing technologies focused on the exploitation of low-grade ore bodies. Cheap energy availability and increasing labor costs in the 1920s found many mining companies in the western United States developing the huge open-pit mines which are a familiar feature of landscapes in Arizona, Montana, Utah, Nevada, and northern Mexico.