In 1896 when Sheridan was a dusty town of perhaps a few hundred people, a team of federal surveyors arrived at the Burlington railroad depot there bent on establishing the precise location of the middle of nowhere.
Sheridan was considered the middle of nowhere because two transcontinental triangulation surveys — part of an effort to determine precisely what lay west of the Mississippi — had bypassed Wyoming in favor of Montana and Colorado. As the U.S. Geological Survey sought to fill in the blank, its leader, Henry Gannett, required field workers to first establish a verified starting point that could be related to known locations — survey markers — in the rest of the country and, ultimately, around the globe.
Caped surveyors with strange looking telescopes, tripods and journals disembarking in Sheridan that summer likely contrasted with the hardscrabble residents. But by the time they completed their task, they’d proven their metle by accomplishing a feat of extraordinary precision across hundreds of miles of hostile landscape.
They laid out a network of two-dozen benchmarks — points to which they assigned global coordinates — from Sheridan to the base of the Teton Mountains in Jackson Hole. Their network became the foundation of the 7.5-minute topographical quadrangle maps of northwest Wyoming still in use today, (Yellowstone National Park was mapped starting from a point in Montana) part of a Geological Survey campaign to map the nation. The government completed that job in 1992, just 9 years before Google Earth made topo maps almost obsolete.
Today anybody with a computer can see a satellite image of the tree that’s grown over the monument where the 1896 survey began. It’s a brick pillar slightly higher than three feet, at the corner of Sheridan’s Crook and Fourth streets. The Sheridan Astro Station monument is largely forgotten. It looks like an orphaned gatepost and has been used as a pedestal for a birdbath. At one point, skateboarders grinding on the pillar knocked off its eight-inch thick capstone. But the monument still stands and has launched pilgrimages by history buffs.
120 years earlier it was the starting point of an entirely different kind of expedition, one in which USGS surveyors crossed 198 miles of untracked mountains and hilltops. Their route took them from Sheridan to Jackson Hole where double checking revealed their measurements were off by only 8 and 11/32nds of an inch.
Six weeks of stargazing
The remarkable accuracy of an 1899 map of Jackson Hole launched Jackson surveyor Todd Cedarholm’s pilgrimage to Sheridan. You might call Cedarholm, the owner of On Sight Land Surveyors, Inc., a cartophile — one obsessed by and in love with maps. When he got to Sheridan he found the monument very much the way surveyors first described it in an annual report — “a solid column of cemented brickwork, 2 by 2 1/2 brick-lengths in cross section and 3 feet in height … capped by a dressed stone measuring 8 by 20 by 24 inches.” Constructing it was their first task. Atop it they centered and embedded a benchmark.
Next, they had to determine where exactly it was.
Doing so was a leapfrog affair. One method of determining where it was would have been to survey from known points hundreds and hundreds of miles away. A faster method was for surveyors to search out known stars with their transits — powerful telescopes with reticles or crosshairs — and measure the stars’ angles above the horizon. The monument pier and benchmark served as a platform for these transits.
Because the crew would spend weeks at the Sheridan monument, they constructed a hut over the pier, with a north-south slit in the roof, Cedarholm said. With all that assembled, the crew’s first task was to determine the orientation of a true meridian — a straight line through the benchmark that ended at the north and south poles.
Establishing a meridian was a relatively simple task, as was the next step — discovering the latitude of the Sheridan monument. It’s done by picking a pair of known stars — one north and one south of the zenith of the astro station — and comparing their angles above the horizontal plane when they passed the meridian. Books and tables provided the star pairs, methods and formulas.
All of this was done at night and so stargazing was the genesis of the Sheridan station’s moniker. The survey crew, Cedarholm observed, “were astronomers more than they were surveyors.”
But determining longitude of the Sheridan Astro Station was more difficult. For this, the crew employed a specialized three-foot long “meridian transit.” As its name indicates, this telescope could point only along the benchmark’s north-south line.
Surveyors would position it in anticipation of a particular, known star crossing its path. When that star lined up in the crosshairs, a surveyor would note its elevation, or vertical angle, and the time. Using formulas, one could calculate how far east or west the Sheridan Astro Station was located.
But the time had to be extremely accurate, and the watches of the day were not up to the task. That’s why Sheridan, a town that was reached by a rail line only four years earlier, was so important.
Along with the railroad came a telegraph wire. Surveyors built the monument 400 feet from the depot so they could connect with colleagues at an observatory in St. Louis, 962 air miles away. Not only were the St. Louis observatory coordinates precisely established, but observers there kept the exact time. With such resources, Sheridan surveyors could eventually determine the longitude of their monument.
But all that timekeeping would take time — six weeks in fact. “These guys had a lot of patience,” Cedarholm said.
Here’s how it worked. The teams in St. Louis and Sheridan would coordinate regarding what stars they both might observe on a particular night. Using various telegraph codes and patterns, surveyors would compare when a star crossed the known St. Louis meridian with when it crossed the unknown longitude at the Sheridan Astro Station.
The surveyors made their observations at both points on the same nights, coordinating and communicating the exact time over the telegraph, Cedarholm said. The time it took the signal to cross hundreds of miles of copper wire was insignificant. Harder to compensate for was the “personal equation,” or how quickly individual telegraphers could hit the key.
The sky had to be clear at both ends of the system and the telegraph wire had to remain intact. “They were really lucky if it worked at both places,” Cedarholm said.
The 1896 field crew determined the Sheridan Astro Station was at 44 degrees 48 minutes 31.10 seconds north latitude, plus or minus 0.12 seconds; 106 degrees 56 minutes 45.21 seconds west longitude, plus or minus 1.16 seconds.
Baseline to baseline across 198 miles
The 1896 surveyors had to establish more than a single point at Sheridan, however. To accurately map the region cartographers needed a network of about two dozen fixed points between Sheridan and Jackson Hole, most on mountaintops.
Surveyors created such networks using triangulation, a mapping system in which multiple survey points are related to one another as a series of connected triangles. Distances — sides of the triangles — are calculated using “classical spherical geometry,” Cedarholm said. In such networks, however, it’s critical first to establish a baseline — one precisely measured side of one triangle.
For the network starting in Sheridan, the surveyors went a short distance to Ranchester where the Burlington and Missouri Railroad ran along a relatively straight and even grade for about five miles. They brought out a 300 foot steel tape. Even the heat of the day could expand the tape and result in inaccurate readings.
Consequently, “measurements were made at night, or during light rains, to avoid so far as possible errors…” the 1897 report said. “Temperature was taken by two thermometers at each tape length.”
Once the survey crossed the mountains to Jackson Hole, surveyors established a second roughly 5-mile baseline at a meadow now known as Baseline Flat. Now it was possible to measure the Teton baseline two ways. One was to take all the readings from Sheridan — 198 miles and 24 mountaintops away — and calculate the baseline length using classical spherical geometry. The second was to mow a path through the sagebrush, get out the 300-foot steel tape and thermometers, and measure the baseline directly.
They did both.
The two measurements of the Teton baseline came within 8 11/32 inches of one another, according to computations made from metric survey reports. That amounts to an error of 1/34484.
What would a contemporary measurement be, Cedarholm wondered.
He took his modern tools to the Teton baseline and measured it himself. “My GPS measurement fell between the two,” he said.
It’s unremarkable that 1896 surveyors could measure a five-mile line with a steel tape and come close to a contemporary measurement. But being able to come within 9 inches of calculating that same distance from 198 miles and 24 mountaintops away reveals the accuracy of the 1896 team and its equipment.
Somewhat confounding to Cedarholm, however, is the actual location of the Teton Baseline — and the Sheridan Monument — on the globe. While the surveyors were precise in their 198-mile exercise, they were less exact in pinpointing the starting point at the Sheridan Astro Station.
Ultimately, the Astro Station — and the corresponding Teton Baseline — are some 1,000 feet off from where the 1896 crew calculated them to be. Most of the difference is in longitude, Cedarholm said. He observed that difference only after setting his GPS device on the Jackson baseline and near the Sheridan monument for several hours each. (Cedarholm couldn’t receive GPS signals at the Sheridan Astro Station because of the overhanging tree, so he computed and corrected from just across the street.)
“I was kind of disappointed,” Cedarholm said. But when put in the context of the entire globe, a 1,000-foot deviation is akin to the few inches difference between the two 1896 Teton baseline measurements.
For the record, Cedarholm calculated the Sheridan Astro Station at N 44 degrees 48 minutes and 21.26463 seconds north, 106 degrees, 57 minutes 5.48893 seconds west.
One crucial piece of topographical information remained to be determined, however — elevation. But that wasn’t in the 1896 job order and it’s not part of the story of the Sheridan Astro Station.
Officially, the USGS lists the Sheridan Astro Station as “presumed destroyed.” But the pillar at corner of Crook and Fourth streets in Sheridan stands proud, and Cedarholm hopes to officially reestablish it with the government as a monument to the middle of nowhere.