The best way to avoid crowded trails? Time travel. Seriously: When land managers stop maintaining mining routes or hiking paths, those passageways go “extinct” and often get excluded from modern maps. Luckily, the U.S. Geological Survey’s (USGS) topoView online database stores maps from as far back as the 1800s, providing experienced hikers with a time capsule of forgotten adventures—including these four.

Prep Work

These hikes can be risky if you lack a high level of backcountry expertise, says Joe Griffith, director of the Colorado Mountain Club’s Wilderness Trekking School. A few things to know before you go:

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1. Don’t head off-trail without knowing how to navigate sans iPhone or cellular network. “The fundamental navigational tools are a map and compass,” Griffith says, “because they are so reliable.” Many outfitters, like REI, offer classes for beginners. Griffith also recommends taking the Colorado Mountain Club Intro to Hiking Safety course.

2. Extinct trails fade away slowly but can still be safe for accomplished explorers. Closed trails, on the other hand, are paths that were shut down for a specific reason, such as protecting wildlife in the area or because conditions are too dangerous for hikers. If you’re not sure which is which, call the U.S. Forest Service or Bureau of Land Management to check.

3. Pay close attention to the weather conditions typically seen in Colorado’s mountains. “In summer, a climber scaling high peaks should know how to evade lightning,” Griffith says. “In winter, an off-trail hiker must be able to avoid avalanches.” Finally, take special care to respect the land as you explore it by following Leave No Trace principles.

Skaguay Power Plant

An “extinct” trail to the ruins of the Skaguay power plant. Photo by Jacob Sells

Completed in 1901, the Skaguay hydropower plant was reachable via horse trails and bridges along Beaver Creek. Floods took out most of the bridges, but those willing to wade through the creek can still use the Big Bull Mountain map from 1951 to make the 11.4-mile out-and-back trek to the ruins. Pick up a state wildlife area pass (or a hunting or fishing license) to legally be on the first part of the trail.

Upper Piney River

From Piney Lake just outside the Eagles Nest Wilderness, the established Upper Piney Trail heads northeast along the Piney River until it makes a sharp bend southeast. Not ready to end your quest north? A single 2013 U.S. Forest Service map shows the trail heading all the way up the valley. A web of bushwhacked trails, including this route, leads to views of the Spider, an impressive 12,692-foot peak at the head of the valley. You can hike about half a mile all the way to its base.

Weehawken Extension

Today’s maps show the switchback-laden Weehawken Trail, an out-and-back starting at the Weehawken trailhead near Ouray, petering out after 3.6 miles. According to USGS maps from 1948, though, an unmaintained trail continues for nearly another mile, revealing views into a basin where elk frolic come summer just beneath Teakettle Mountain and Potosi Peak.

Orphan Boy Cabin

Likely built in the late 1800s by miners in the Gore Range, the cabin sits in a basin northeast of Keller Mountain and was undisturbed until the 1950s, when ranchers found it. Take a two-mile trail—once used to reach mines and visible on the 1929 Dillon USGS map—that climbs the east ridge of Keller from the Gore Range Trail between the Boulder Lake and Rock Creek trails.