The body of 54-year-old Jennifer Nelson, of Ridgway, was found at the bottom of a deep and water-filled mine shaft along Red Mountain Pass on the morning of October 21, reports the Ouray County Plaindealer. Nelson had been reportedly missing the night before, discovered when dogs that had been with her were later found lingering in the area of the pit.

According to the Ouray County Plaindealer report, Nelson had been hiking in the area of Spirit Gulch, which is located in Uncompahgre National Forest. The pit Nelson fell into was located about 50 feet off a mine access road in the area, with her body found about eight to 10 feet down the shaft.

The hazard of abandoned mine shafts is prevalent in Colorado’s mining country, with many of these shafts being gated or capped once discovered. That said, mine shafts in unknown locations do exist and can be difficult to see or can be overgrown to the point where they’re hidden but still unable to support weight. In some cases, mine shafts can also have makeshift covers that were installed many decades ago and have been left to decay.

A report from Olivia Prentzel at the Colorado Sun indicates that around 14,000 abandoned mine openings have been sealed in the last 40-some years, though it’s believed that thousands still exist.

At last report, Nelson’s cause-of-death was still being investigated. It’s not just the fall risk that comes with slipping into a mine shaft though. Frigid water that sometimes fills the shafts can also be deadly, as can toxic gas. It’s also worth noting that snowfall can hide unmarked holes, as well, making it even more difficult to know where mine shafts might be (find some historical examples of deaths that have occurred in Colorado’s mine shafts here).

When it comes to safety when exploring Colorado’s mining country, avoid abandoned structures, stay on established routes, and avoid traveling alone.

Read the full report on the situation from Ouray County Plaindealer here and for a deeper dive into the hazards associated with unknown mine shafts, check out Olivia Prentzel’s piece on the subject, featured on the Colorado Sun website.