Willoughby: Underground, in the dark, in four dimensions

My father could sense his whereabouts underground as well as his position in relation to the surface — at least when he stood within the Midnight Mine, his domain. He could not refer to mountains, valleys and other visual landmarks to determine his location. Instead, as he strolled along a tunnel, he observed the rock. Just as different houses and trees mark a position along a city block, my father recognized the changes in rock type that characterized a specific site in Aspen’s tunnels.

Such intuition, no matter how useful, must be verified when you aim a tunnel toward a distant location. The Midnight tunnel traversed a mile and a quarter. The slightest deviation in direction could compound over distance, and a tunnel to the wrong place could result in cost overruns or even catastrophe.

Aspen’s largest mineral veins extended only 50 or 60 feet from side to side. To target such a vein would resemble a search for the bandstand in Paepcke Park — from the length of a football field away, minus the end zones, in total darkness. If you walked a straight line, but angled a few degrees off course, you would bypass your destination.

Mining engineers and surveyors completed detailed surveys to improve their underground navigation skills and precision. But even untrained prospectors could handle the math with the help of a Brunton compass, designed by Aspen local D. W. Brunton. The tool approached the accuracy of a transit and provided additional benefits in the dark.

Miners plotted their underground wanderings on flat maps, through tunnels that followed a three-dimensional reality. The tunnels followed the horizontal vagaries of geology and transected multiple vertical levels. And keeping track of location underground involved one additional dimension — underground surveys had to sync with surface surveys. Builders of the Midnight tunnel learned this lesson the hard way.

The Midnight tunnel aimed toward a specific location, the presumed downward extension of the ore vein that had been mined in Little Annie Basin during the 1880s and 1890s. The former, collapsed, Midnight shaft ended at a depth of 500 feet. Yet after years of tunneling from Queens Gulch toward that spot, modern Midnight miners did not find the shaft. Perhaps they had misidentified the location and lost the value of all their work and investment. Or perhaps a survey error had led them astray.

My grandfather Fred D. Willoughby, the mine CEO and engineer, charted the tunnel with a Brunton compass each day. Other workers resurveyed his work and found it correct. This confirmation left one remaining explanation for why the new tunnel had not connected with the end of the old shaft. The underground survey had been predicated on a surface survey. Perhaps the surface survey, completed by a contractor in previous years, confounded them.

The question of the surface survey’s accuracy arose in winter, so miners had to wait until spring to survey the surface. Eventually, a new surface survey indicated that the old one deviated by 200 horizontal feet. The company adjusted the tunnel direction accordingly and reached the intended location.

The precise description of an underground location resolved issues greater than the quest for a dilapidated mine shaft. Just as neighbors above ground may battle over the location of a fence relative to their property lines, miners also fought for their property rights. If one mine dared stray onto another mine’s claim in the dark underground, an accurate survey would shed light on the trespass above ground, and in court.

Tim Willoughby’s family story parallels Aspen’s. He began sharing folklore while teaching Aspen Country Day School and Colorado Mountain College. Now a tourist in his native town, he views it with historical perspective. Reach him at redmtn2@comcast.net.