Aspen at a scale of 1 to 9,600 |

Aspen at a scale of 1 to 9,600

Tim Willoughby
Aspen Times Weekly

When prospectors flooded into the Roaring Fork Valley in 1879, they no longer depended on Native American guides as Lewis and Clark had a few generations before them. The new seekers of fortune carried detailed maps that showed streams, mountains and geology. Aspen continues to this day as one of the best-mapped areas of our country, thanks to the employees of the United States Geological Survey (USGS), whose cartographic creations are as beautiful as they are informative.

The Hayden Survey (1873) came to Aspen first, producing maps of sufficient scale and accuracy to allow adventurers to navigate roadless regions and to locate areas of geological interest. The Hayden Survey includes hand-drawn pen and ink panoramas from the tops of Colorado’s peaks, including one of the Elk Mountains. Compared to photographs from the same locations, the drawings reveal more interesting details.

Today’s perfect maps rely on satellite imagery and GPS technology. Mapping of the 1870s relied on the plane table, a simple invention. The mapper set up a measured base line of a few hundred feet. Distant objects, river bends, mountain tops, etc., were then sited from each end of the base line through an unmagnified viewfinder. The viewfinder rested on a ruler that was placed on paper on a portable table. With each sighting, the mapper drew a line on the paper. Where the lines crossed, the object was located, at scale, on the map. Along with triangulation surveying using a transit, detailed maps were produced.

Josiah Edward Spurr mapped Aspen’s geology at the amazing scale of 1 to 9,600. Spurr and his assistants did their fieldwork in 1895-96 then headed off to the Yukon gold rush. The USGS published the monograph of geologic interpretations and the accompanying atlas in 1898. Lithographer Julius Bien and Company of New York printed the atlas. The colorful pages of Spurr’s atlas bedecked Aspen’s offices and lodges in the 1970s.

Spurr explored geology from within Colorado’s mines, working his way literally from underground up. His maps and conclusions rival modern geologic mapping. Viewing the pages of the Spurr atlas, it is amazing to see how many faults bisect surrounding mountains. In the Tourtelotte Park area on Aspen Mountain, fault lines crisscross every hundred yards.

Bruce Bryant’s most recent USGS topographical mapping of Aspen was published in 1972. That study and eight maps at a scale of 1 to 24,000 provide fascinating information. The building hazards map caused some consternation when owners of undeveloped property discovered the reason why previous generations had not built on steep slopes of glacial deposits sitting on angled bedrock. While Bryant’s avalanche potential map dissuaded building in some locations, his maps of potential groundwater encouraged development in others.

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Bryant’s geological maps detailed areas that were not mineralized and therefore not examined as carefully by Spurr. My favorite Bryant map shows ” mines, prospects, and areas of significant silver, lead, and zinc production.” That map illustrates hundreds of shafts, tunnel adits and prospect holes. It is useful to carry when you are exploring Aspen and Smuggler mountains. The prospect locations are often only small cavities where miners drilled into bedrock, chasing mineralized material just far enough to conclude that it led to no profitable vein. By the 1970s, many of the shaft and adit holes had already filled in to the point where they were hard to find. Perhaps today only diggings in hard rock remain visible. Nevertheless, a vicarious tour of Aspen’s unique geologic history remains easily accessible through the Hayden, Spurr and Bryant maps.