WESTFIR, Ore. - A 200-foot-deep rift in the forest floor, deep enough to hold a 20-story building and create a subterranean climate at least 20 degrees cooler than summer temperatures above, has deliberately been kept out of tourist guidebooks.
Its caretakers don't want people stumbling into it unprepared, or making the hour-long descent to its bottom only to be buried by one of the periodic showers of rocks and boulders from its crumbling basalt walls.
It's known as the Hell Hole.
"It's more than a hole; this thing is a half a mile long," says U.S. Forest Service geologist Mike Long, making his 12th trip into the Hell Hole over the past 15 years.
He learned of the geologic anomaly from his predecessors at the Forest Service. It's been omitted from government maps since the 1930s, when it was marked on the charts used by loggers.
By Long's count, on his first climb into the Hell Hole he joined an exclusive fraternity of just six Forest Service employees who had been to its bottom. The club hasn't grown much since.
The government can't legally prevent the curious from entering the canyon. It's on public land, surrounded by 40 acres of woods designated by the Willamette National Forest as a special-interest area to protect it from logging or development.
Keeping the location secret is more a matter of protecting the public from itself. Roughly speaking, Hell Hole is in the highlands above the North Fork of the Middle Fork of the Willamette River.
"Even (for) experienced climbers or rappellers, I don't think this would be a good place for sport climbing," Long says. "It doesn't take very much to kill yourself down here."
Hell Hole's geologic origin can be traced back 2 million years, when lava flows oozed into the upper North Fork Valley from a series of fissure eruptions.
The flows created a formation of new lava cradled by flows from earlier eruptions. Much more recently, a progression of glaciers moved through the valley and destabilized the base upon which the newer lava rested.
The eventual product was the Hell Hole.
What you won't find
The hole also is surprising for things that haven't shown up in scientific examinations.
Even though it's well into the Cascade snow zone, there's no streambed or any other indication of spring runoff at its bottom. "The (olivine basalt) rock and soil are so permeable, it soaks it up like a sponge," Long says.
Even in the dead of summer, large spans of its silt-encrusted walls remain muddy. Moss and small, dangling ferns cover the rocks on the shadier east wall. On a hot day, steam rises from the backs of hikers as they reach the coolest layer of air on the canyon bottom.
Another peculiarity is that no animal carcasses have ever been found in the hole.
"Whether they've been covered up (by erosion debris) or they're just smarter than we are, I don't know," Long says.
There was talk in recent years about putting a fence around the Hell Hole, maybe even running a footbridge over its top for public viewing. That didn't rise far on the agency's priority scale.
About the only thing now in the works is a plan to install laser devices on each side of the rift to take exact, periodic measurements of how much, if at all, the gap is widening.