Walker Mine

Reports vary, but the deposits worked by the Walker mine are said to have been (re?)discovered in 1909 and then worked from 1911 to ca. 1943. The primary product was copper, an important industrial metal by the early 20th century. A mill on-site processed the ore into concentrates, which were then shipped out for further processing into copper metal (and byproducts such as silver). A company town, Walkermine (spelled as one word), housed the workers and their families. The concentrates were shipped to the Western Pacific Railroad, a transcontinental route on the other side of Grizzly Ridge to the south. (The railroad still exists and is now part of the Union Pacific. It is paralleled by California State Route 70.)

Transportation was not a problem in the summer months. However, heavy snow cover in the winter blocked the roads—evidently plowing the roads was uneconomic at the time—so a tramway was constructed over Grizzly Ridge to avoid having to shut down the operations completely during the snowy season.

The tramway ran from the mine to Spring Garden, about 9 miles southwesterly. The tram carried ore concentrates out, but also carried personnel and supplies both in and out. The tramway alignment is still shown on the 1972 edition of the USGS 7.5' Mt. Ingalls quad, even though the tramway had been removed long before then. The tramway towers were wooden, and some of them survived for decades, but they were largely destroyed in the 2021 Dixie Fire.

The mine was abandoned when the deposits dwindled, and unsurprisingly, there was no concern about legacy pollution in those days. The mine area was just left to its own devices with no attempt at reclamation. The usual source of pollution in these sorts of ore bodies is so-called acid mine drainage, when sulfides remaining in the rock oxidize to sulfuric acid in the presence of oxygen and water. The increased acidity, not surprisingly, can kill most aquatic life. A secondary effect is that the acidic water leaches materials from the rock, which commonly results in high dissolved concentrations of toxic heavy metals.

The mine itself is also not the only source of pollution; the mill tailings are too. "Tailings" are the crushed rock that's been through the mill. They always contain some missed ore minerals because the separation isn't perfect, as well as other minerals including worthless sulfide minerals (the "gangue") such as pyrite. Because the tailings are so fine-grained, they are even more reactive than the raw rock. The tailings also cover a large area; in fact, the tailings flat from the old mill is prominent in Google satellite photos.

Remediation efforts, therefore, had to address the tailings as well as the mine itself. Ultimately the reactive materials had to be isolated from water and oxygen, and any drainage from the mine and tailings had to be contained and/or rerouted. Unsurprisingly, there was lots of legal maneuvering over the years, focusing on who would be responsible for paying the remediation costs. According to the Central Valley Regional Water Board, the Walker Mine is now a "success story." Let's hope it stays so.