Surveyors faced obstacles but had geometry on their side.

Soon after the Civil War ended, the United States began a major national surveying project, its object to measure a line of latitude (the 39th parallel north) across the continent. The project required the establishment of stone survey stations atop some of the West’s highest peaks, despite the risk posed by fierce summer thunderstorms. Indeed, crews complained about“the most violent electrical discharges and thunderbolts imaginable,” peaks that “fairly hummed or hissed by virtue of escaping electricity” and the way “sparks a couple of inches in length could easily be drawn from any exposed insulated object.” Lightning struck three members of one survey party and demolished their tent and equipment. Most surveyors would simply cower beneath rock ledges well below the summit to avoid the lightning.

Nearly 150 years later the foundations of their stone survey stations remain atop many Western peaks. In a process called triangulation, surveyors measured the angles between these fixed points over vast distances, allowing for accurate plotting without having to actually measure every foot of ground. While the surveyors faced a tremendous task in carving out trails and hauling equipment and supplies up these mountains, it meant a lot less work in the long run.

After the Revolutionary War, Congress set aside land west of the original 13 colonies either to reward veterans or for sale to pay off war debts. The land would have to be surveyed, so Thomas Jefferson proposed a rectangular Public Land Survey System that created a series of 6-squaremile townships divided into 36 square-mile sections. Federal survey teams plotted the West (except Texas), the Midwest and most of the South using this system. But they first needed to establish broad baselines, hence the transcontinental survey projects.

In 1807 Congress established the U.S. Coast Survey to plot America’s coastal waterways. As the country grew, the agency was renamed the U.S. Coast and Geodetic Survey, its mission expanded to survey America’s interior. From 1871 to 1898 USC&GS surveyors conducted the first great Transcontinental Triangulation, plotting a control line along the 39th parallel for 2,750 miles—between the Cape May, N.J., and Point Arena, Calif, lighthouses. The lines of measurement were so long that surveyors had to factor in the Earth’s curvature, introducing an error of 1 foot every 34½ miles.

Conducted primarily to coordinate surveys already done on the opposite coasts, it also served to provide control points in the states through which it passed. The 39th parallel practically bisects the West (passing just south of Denver and Salt Lake City and straight across Lake Tahoe) and remains a key control line for today’s Western surveys.

Triangulation is a particularly effective way to measure linear distances, especially across difficult terrain.Teams measured the angles using a theodolite—a surveyor’s instrument comprising a small telescope that pivots on two axes measured in degrees. It is based on simple geometry. Consider the figure below:

In this series of connected triangles, each triangle contains a baseline shared with the adjacent triangle; line AB serves as the baseline of the triangle ABC, as it is easiest to measure on the ground. Each corner of each triangle must be visible from its other two corners (hence the placement of stations on high mountain peaks). This line of sight enables easy measurement of any two angles—say angle A and angle B. As the sum of all three angles must equal 180 degrees, one can calculate angle C using subtraction. Simple geometry, in turn, provides the length of the other two sides of triangle ABC. At that point, line BC becomes the baseline of triangle BCD, and the process repeats. Once the survey team determines the length of line EF, it would check that measurement on the ground to ensure it meets the required levels of accuracy. Only two lines need be measured on the ground—one at the beginning and one at the end.The resulting series of triangles is called a triangulation system or network.

Shown in the diagram below is the section of the Transcontinental Triangulation from Salt Lake City nearly to the coast of California. Ogden Peak is near Salt Lake City; Diamond Peak is near Eureka, Nev.; Lone Mountain is near Tonopah, Nev.; Pah Rah is near Pyramid Lake and Reno; Round Top is a Sierra Nevada peak; and Mount Tamalpais is just north of San Francisco’s Golden Gate. Note the series of geometric figures, mainly triangles. Triangulation made it possible to measure these open spaces from the survey stations.

The Great Basin, with its widely spaced mountain ranges running north-south, was ideal for triangulation. Some crests were visible for 100 miles and allowed for surveying on what many described as “an unusually grand scale.” The rough weather at elevation usually meant that survey teams could occupy only two such peaks in season (roughly June to November), though October storms often trapped teams in the mountains. A snowstorm on Wheeler Peak almost buried one team in 12-foot drifts, with temperatures plunging to 20 below zero. To continue their observations, teams would sometimes have to cut deep and broad trenches through the snowdrifts along the line of sight. The Sierra Nevada was a particular challenge, its high peaks offering ideal sites for stations, though the range itself presented a major obstacle along potential sighting lines.

The highest Western peaks allowed for some very large triangles, with sides stretching nearly 200 miles. Pinpointing a target at such great distances was extremely difficult, but surveyors solved that problem with use of a heliotrope, a surveying instrument with a mirror that reflects sunlight in a powerful beam easily discernible to the naked eye at 150 miles or more. “On long easterly and westerly oriented lines, the curious phenomenon of getting the reflected sunlight thrown to the station at which the sun was already below the horizon was frequently observed and at times lasted several minutes,” noted the 1900 USC&GS special publication The Transcontinental Triangulation and the American Arc of the Parallel. According to the same publication:

Lower camps were established at the end of transportation by wagon, and a pack trail was located and opened to the upper camp, usually distant 5 to 10 miles, and involving much cutting of fallen timber, grading and blasting or quarrying of rocks; the ascent was usually between 3,000 and 7,000 feet. Ordinarily about 10,000 pounds of outfit, instruments and provisions had to be transported to the upper camp— usually two weeks’ labor—for which purpose from five to seven pack mules were employed, each carrying as a load about 150 pounds—rarely and exceptionally as much as 200 pounds—according to the length of the trail, steepness and height of ascent. The transportation of the great theodolite, weighing with packing box about 200 pounds, required from one to two days. Sometimes it was carried by hand; at other times it was drawn by a horse and guided by men. This was accomplished by men…guiding it while a horse was pulling it by means of a rope.

The preparatory work to put the mountaintop in condition for occupation was usually very considerable. The instruments were mounted on masonry or rock, the observer stood upon a raised floor, and whole was walled in and surrounded by a stout canvas tent to order to break the force of the wind.The theodolite stood upon its iron position stand and was effectively protected against the direct sunlight and radiant heat by the double-walled and double-roofed observing tent. As the occupation of a station covered about one month only, two principal stations a year could be disposed of, since the favorable season lasted but four months.

Occupying each station were three officers and a recorder, plus assorted packers, drivers and cooks. Heliotropers, or flashers, manned distant stations in pairs and numbered from 10 to 20. They lived in tents, stone cabins or dugouts close to the actual stations. Many heliotropers used secondary mirrors to communicate between stations via heliography, using Morse code.

Indians were frequent visitors at the survey camps, especially in Colorado and Nevada. “Their demeanor was uniformly unobtrusive and considerate,” according to the 1900 report. The survey teams sometimes hired them to pack wood and water. In 1878 teams on the Nevada section of the survey hired famed naturalist John Muir as a guide, in turn enabling Muir to explore the Great Basin and its loftiest peaks. The station ruins remain as ghosts of a Western enterprise few even realize existed.


Originally published in the August 2011 issue of Wild West. To subscribe, click here.