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Mount Shasta Triangle and Davidson Quadrilateral





















MT SHASTA (USGS Station. The original CGS station is not published.)

Pacific Coast surveys

By 1879, the U.S. Coast and Geodetic Survey had been practicing the science of triangulation for over 60 years. During that time, the nation had grown from a union of Eastern and Ohio Valley states to a nation that spanned the North American continent. Each expansion of the nation had given the Survey new responsibilities and challenges.

Acquisition of the territory of Oregon (1846), the state of California (1850), and the Alaskan purchase (1867) brought the Survey the challenge of mapping the Pacific coastline. In addition, the continental interior had been opened by settlers and railroads, and Congress had recently approved the transcontinental triangulation. The survey networks along the Pacific coast which had been established over the last 25 years now needed to be extended into and over the Sierras, and the man who found himself at the forefront of those efforts was Professor George Davidson.

Davidson's scheme

Professor Davidson had joined the Survey in 1845 as a twenty-year-old former student of, and assistant to, newly appointed Superintendent A. D. Bache, and soon became a recognized expert in the techniques and instruments of triangulation. In 1850 he was sent to San Francisco to begin mapping the coastlines of the new state, measuring its tides and currents and scouting locations for lighthouses. There he worked until the onset of the Civil War, when he was recalled East to assist the Union with coastal blockades and strategic mapping. Returning to the Pacific Coast in 1867, Davidson resumed his work, concentrating on harbor and coastal surveys and mapping.

When Congress authorized the transcontinental arc of triangulation, Davidson began plans to carry the coastal surveys into and across the mountains of California. Shasta, the high volcanic peak that dominates northern California, seemed a likely candidate for use as a geodetic point and for use with topographic surveys throughout the region. Lack of funds prevented progress until 1874, when William Eimbeck and T. J. Lowry were sent to reconnoiter stations that could connect the summits of the Sierra Nevada with the coastal network.

Eimbeck's reconnaissance

William Eimbeck was a 33 year old German immigrant who had received an engineering education in St. Louis. There he found employment on the Eads bridge project and in the city engineering offices. In 1869 he volunteered to observe solar eclipses for the Coast Survey and earned the attention of the Assistants in charge. He was invited into the Survey in 1871 and joined the transcontinental triangulation then in progress in Missouri. Assigned to the Pacific coast in 1872, he worked on coastal triangulation and astronomic observations. When Davidson needed a man to locate stations for the Sierra triangulation, he chose Eimbeck.

Keeping an eye on lines to Mount Shasta, Eimbeck first investigated points west of the central valley of California at Diablo, Vaca, and Snow Mountain. Vaca had lines to the Sierras but not Shasta. Snow Mountain had a point on the northern summit with a sight line to Mount Shasta, but the location was extremely rugged and inaccessible. Moving eastward, he found additional lines at Marysville Butte, Pilot Hill, and Pine Hill. Finally in June of 1875 Eimbeck ascended Lola Mountain in the Sierras and spied Shasta standing 167 miles distant. Eimbeck had found the stations needed for a great quadrilateral that stretched 130 miles across the Sacramento Valley, and which formed the base of an enormous triangle containing Mount Shasta.


Shasta signal

Meanwhile Davidson had dispatched A. F. Rodgers to the summit of Mount Shasta to determine its suitability as a geodetic station. Accompanied by famous naturalist John Muir, Rodgers explored the summit on April 28th and determined that construction of a signal visible to the south would be practical, although difficult due to the altitude and rough terrain. On April 30th, Muir again ascended to the summit with mountaineer Jerome Fay to make barometric observations while Rodgers remained at the base to take simultaneous readings at agreed times. Soon after their last scheduled observation at 3:00 pm, Muir and Fay began their descent but were overtaken by a snow storm that stranded them on the mountain overnight and threatened their lives. For seventeen hours they huddled for warmth next to steaming fumaroles, risking asphyxia from the fumes. The next morning, suffering from both burns and frostbite, they fought their way through two feet of fresh snow to find their way back to camp. John Muir later wrote of the ordeal in an article for Harpers Magazine published in September 1877 with the title "Snow-Storm on Mount Shasta."

At the end of September 1875, Rodgers returned to Shasta to erect a permanent signal. The signal was a unique design, a ten foot tall 2-1/2 foot diameter tube constructed of plate iron segments, topped with a 3-foot parabolic conoid of nickel-plated copper. The polished nickel would reflect sunlight to distant observers, saving the necessity of stationing heliotrope operators at the summit, a job that would have been excessively hazardous due to the 14,200 foot elevation and exposure to the elements. The 3,500-pound monument was broken into 26-pound sections and hauled by mules to the 11,000 foot level, then carried to the summit on the backs of Indian laborers. After 7 days the pieces had all arrived at the summit and assembly began. Construction was completed two days later on October 7. During construction the entire party suffered from headaches and inability to sleep, an effect of the altitude.

The observations begin

With a permanent signal on Shasta and the reconnaissance in the Sierras complete, it was time for the triangulation across California to begin. The first observations occurred in the summer of 1876 at Mount Diablo, and the angles to the stations of the Davidson Quadrilateral were completed by September. Then the instruments were moved to Mount Helena.


The summit station at Round Top, 1876 (NOAA Photo library)

The difficulties at Mount Helena foretold the trials to come as triangulation parties entered the mountainous West. High winds flattened the party's tents and knocked men off their feet. The winds were countered by surrounding the observing tent with a five foot high stone wall, protecting the instruments inside from destruction. Then came October rains, dumping seven and half inches on the summit. The same storm left the Sierra stations enveloped in snow, prompting the heliotropers at Lola to abandon their post in fear for their safety. Fortunately, two heliotropers at Round Top remained steadfast and allowed Davidson to complete observations to that station by November 6. Then within seven days and "by great industry" the two heliotropers transferred to Lola and allowed Davidson to complete the readings on November 27. All together 1,778 horizontal angle readings were taken on twenty-two objects from Mount Helena. From Mount Diablo, 1,596 readings had been taken on nine stations.

Closing the Davidson quadrilateral

The year 1878 kept Davidson occupied with calibration of the theodolite and performing surveys in Oregon and Washington territory. He also attended the International Exposition in Paris to examine the latest geodetic instruments, returning home with the conclusion that America's instruments compared favorably to the best European ones. Finally, in February 1879 preparations were made to occupy Mt. Lola and Round Top to complete the observations for the Davidson quadrilateral. The theodolite was mounted at the summit of Lola in June. After sixty consecutive hours of snow, sleet, rain, and wind, the weather moderated and observations began on June 18.

The longest line ever observed

While Davidson was occupied on Lola with observations for the quadrilateral, he dispatched Benjamin Colonna to Shasta with heliotrope and theodolite, with full expectation that the sightings on Shasta could finally be accomplished.

36 year old Benjamin Azaria Colonna had been with the Survey for nine years. As a cadet at Virginia Military Institute, he had fought in the battle of New Market, and shortly after graduation in 1864 he received his commission as commander of a Confederate engineering battalion in Atlanta, just in time to cover the army's retreat from that city. The end of the war found Captain Colonna back in Virginia, where he returned to his home on the Eastern Shore to teach. One day, caught on the water during a gale, his boat overturned near where a U.S. Coast Survey party was working. Upon his rescue, he struck a friendship with one member of the party who urged him to join the Survey, which he did in 1870. After working on projects up and down the Atlantic and Gulf coasts, he was assigned to San Francisco in 1877 and reported to Professor Davidson. Field work on coastal triangulations kept Colonna busy throughout 1878. He accompanied Davidson to Lola in the spring of 1879, where he helped prepare the site for observations and then departed for Shasta.

Sisson's inn was the launching point for most expeditions up Shasta. Colonna arrived there on July 18 and made preparations to transport the 750 pounds of instruments up the mountain. Hiring Indians to pack the equipment on foot just as Rodgers had done four years earlier, Colonna began the two-day journey up the mountain on July 24. Camp was established at Hot Springs, about 215 feet below the summit. Although he was accompanied by two assistants, one of them was incapacitated by the altitude, and so Colonna had only one helper when he established the summit station on July 26. Then he waited for the atmosphere to clear enough for contact with Mount Lola and Helena. On July 29, he had a brief glimpse of the heliotrope on Lola, but was unable to take readings. However, Davidson, who was nearly finished with his work at Lola, managed on that day to sight the heliotrope on Mount Shasta and record measurements. Finally on August 1 the atmosphere cleared and Colonna was able to plainly see the signals on both Lola and Helena. The next day allowed additional readings. The success of the expedition was assured, and a new record for the longest line of triangulation was set.


Colonna wrote of his experience in his article "Nine Days on the Summit of Mt. Shasta" published in 1880. Sadly, his career in the field ended in 1884 when he slipped while working on the slopes of Mt. Olympia and was caught in an avalanche of loose rock. Suffering from partial paralysis, he slowly recovered but never regained his full strength. He continued to work for the Survey in the D.C. office until 1895.

Davidson's career with the Survey also extended to 1895, and he remained an eminent member of the scientific community until his death in 1911. During his career he received multiple honors for his work in astronomy, surveying, and engineering and was frequently consulted by government on many scientific issues. He served on numerous committees and held the presidency of the California Academy of Sciences for 16 years.

Rodger's signal at Shasta summit survived until 1903, when a storm toppled it from its foundation. It was later found in the snowfield at the base of the summit pinnacle, too damaged to be restored to service. The cone was recovered and placed in Sisson Museum, where it remains today. (article)

ShastaTriangle (last edited 2009-03-28 20:17:12 by Holograph)