Exposed during runoff from heavy spring snow, the hole could be part of the original Federal Gold Mining Co. production shaft from 1898.
A sinkhole that appeared unexpectedly near the Carissa Mill site in South Pass City may be the previously hidden entrance to the mine's largest historic gold shaft, site historian Jon Lane said.
The hole, within 50 yards of the original Cariso Lode discovery site that prompted the settlement and gold rush at South Pass City, is a jagged maw in the otherwise unruffled side of a sagebrush-covered hill just beyond the mill's elevated mine cart trestle.
Lane estimated that the hole is at least 40 feet deep in its main open section, adding that it likely connects to the extensive, largely flooded network of deep mine tunnels that run beneath the Carissa Site.
Snowfall last winter was at or near record levels in the region. Lane said holes and shafts can be opened up and expanded by severe winter weather.
Specifically, he said, heavy snow can cause runoff water to seep into cracks in the bedrock underlying the hills around South Pass.
If this runoff then freezes again, it expands and breaks up the rock, allowing sediment to slip and slide along otherwise solid hillsides.
The original Cariso site has fallen victim to this in the past, expanding the hole and dropping large boulders deep into its depths from the walls above.
Now, a new shaft has appeared thanks to the bad weather, and it's up to Lane and his team to work with state authorities to address it.
The first thing to do about the new hole, Lane said, is figure out exactly what it is.
Based on his understanding of the area and historic surveys of the mine available in his archives, Lane said the new hole is likely to be one of two sites: the "Iron Shaft," a gold rush-era outfit so named for the red color of the shaft walls dyed by iron staining in their mineral deposits; or the Federal Gold Mining Company's 1898 production shaft, the largest gold producing shaft ever at the Carissa site.
Either shaft would be an exciting prospect, but no matter which it is, the other is not far away. Lane said that the other mine shaft, still covered, is within 15 feet of the now-exposed hole. Both of them must be secured and developed before public access can be considered, he said.
To that end, Lane will work with surveyors from Abandoned Mine Lands and the Bureau of Land Management.
Now that the newly-exposed shaft is discovered, satellite surveys of the present-day site, combined with his archival documents and surveys, can map the location of the shafts to within a quarter inch, allowing surveyors to identify the new hole definitely and locate the still-buried shaft as well.
Then, AML and Lane will work together to secure the area.
Lane said that AML has helped to seal discovered shafts in the area before, and that he will push for the new shaft to be preserved in a way that is both safe for the public and available for them to see.
In an ideal world, Lane said, he would like to have a metal grate installed over the new shaft, so that visitors could stand above it and gaze into the black depths of South Pass's largest historic gold mine.