You have reached the intersection of John’s 99 and Mother Urban trails. The large hotel in the distance is the Montage Deer Valley, built on the former Daly West Mine site. You’ll hear more about this mine further along the trail. You’re still on the Historic Mine Route, so keep following the wayfinding arrows.
Just downhill, Walker-Webster Gulch meets Empire Canyon at a major geologic crossroads in the Park City Mining District. Two important mine drain tunnels emptied here: the Alliance Tunnel and the Judge Tunnel.
To understand why these drain tunnels were necessary, it helps to step back and look at the local geology.
Sherie Harding, PhD, is a local earth scientist with a PhD in geology and specialties in sedimentology and paleontology.
Beneath your feet are ancient sedimentary rocks. The mines of Park City extracted great mineral wealth from these sandstones and limestones. In chapter one of their geologic history, some 300 million years ago, wind-blown sand and coastal reefs existed off the coast of Pangea. Layer upon layer accumulated over time. Eventually, these sedimentary layers were compressed into rock.
In the next geologic chapter, the flat-lying sedimentary rocks were compressed and uplifted through powerful tectonic forces from the colliding plates of Earth’s lithosphere, the hard, rocky outer crust and the uppermost part of the mantle.
These extreme pressures caused cracks to form in the sedimentary rocks. Hot water, rich in silver, lead, and zinc, sourced from magma deep underground, was forced into the cracks, depositing the precious metals. In recent geologic time, further concentration occurred, water percolated from the surface, mobilizing and concentrating the metals into “bonanza” deposits at the base of the weathered zone. The weathered zone is near the surface, where the ground is exposed to water, air, and changing temperatures, making mineral riches easily available.
This also meant that this water, through rain and snow, seeped into the ground in vast quantities. Managing this water flow was one of the principal engineering challenges faced by the miners.
Miners could pump water up the shafts, but the deeper they dug, the more expensive that became. Their solution was to dig drain tunnels to lower-elevation outlets, letting gravity carry water out of the mines. In Empire Canyon, the 4,700-foot Alliance Tunnel drained the Treasure Hill properties, mainly the Silver King Coalition Mine. The 6,600-foot Judge Tunnel drained the Daly-Judge Mine beneath what is now Deer Valley Resort. The Alliance Tunnel is plugged, but the Judge Tunnel still drains groundwater used by the Park City Water Department. Both tunnels are near the Alliance Mine and Judge Mining and Smelting buildings in Empire Canyon, where more audio stories are available.
More Information:
Dr. Harding Lecture: The Period of Explosive Volcanoes