Silver was found at Castle Creek and on Aspen Mountain in 1879. A group
of prospectors from Leadville, apparently after examining maps of the
Geological and Geographical Atlas of Colorado published in 1877,
explored along the line of Paleozoic limestones encircling the Sawatch
Range. As they had hoped, they found ores similar to those at Leadville
in rocks of the same age.
Mining began at Aspen in 1880. Here, as at Leadville, intrusion of
granite porphyry into or near the Leadville Limestone had broken and
deformed the layers, and ores were deposited in fissures and as
replacements during cooling of the intrusions. The intricacy of faulting
which controls the ore pockets in the limestone is well shown on the map
of Aspen Mountain in Chapter II.
Glaciation occurred in this area, and glacial deposits cover most of the
ore bodies and outcrops so that little bedrock is exposed. Mapping was
accomplished by extrapolating to the surface the bedrock patterns shown
in mine pits, shafts, and tunnels.
Aspen produced some of the richest silver ores in the world, and thrived
as a boom town for most of two decades. In 1888 the value of ores
produced reached over $7,000,000; the next year it topped $10,000,000.
After the silver crash of 1893 production declined rapidly; the last
mines were closed in the 1920s. Total production of silver, lead, zinc,
and copper reached about $100,000,000. There was virtually no gold in
the ores at Aspen.