The Transcontinental Triangulation was authorized by Congress in 1871 to measure a coast-to-coast arc along the 39th parallel. The work took nearly three decades, and resulted in the first accurate measure of the continent, and one of the largest arcs ever measured. Among the many results of the triangulation was the selection of the Clarke 1866 spheriod as the best fit to the continental United States. The arc also provided the foundation for a national datum, and anchored the other great triangulation projects to the nation's heartland. The station Meade's Ranch was first surveyed in the transcontinental triangulation and ultimately became the origin of the NAD27 datum.

The triangulation consisted of 10 base line surveys and 11 separate triangulation series connected to the baselines. In the East, portions of the earlier Coast and Geodetic Surveys from the 1840's were incorporated into the network. At St. Louis, Missouri, the American Bottom base line from the U.S. Lake Survey was incorporated. The majority of the network was surveyed specifically for the transcontinental arc, however, and CGS officers were responsible for the annual parties that slowly made their way across the nation.

The surveyors sometimes endured severe hardships to accomplish their mission. In the mountains of the west the stations were often located on the highest peaks and the teams endured high winds, extreme cold, and dangerous lightning. It was necessary to transport delicate equipment over roadless territory, and then build trails up the sides of the mountains before the equipment could be mounted. The last horizontal angle measurements were completed in 1896. The work of computing the adjustments to the network took another 4 years, and the final report was published in 1900.

Most of the stations that were occupied during the triangulation are still to be found in the NGS database. Details of the base lines and series are found below.

Base LInes

Triangulation Series

[:KentIslandBaseLine:Kent Island base line (1844)]

[:EasternShoreSeries:Eastern Shore series (1844-1848, 1896-1897)]

[:AmericanBottomBaseLine:American bottom base line (1872)]

[:AlleghenySeries:Allegheny series (1846-1850, 1868-1880)]

[:OlneyBaseLine:Olney base line (1879)]

[:OhioSeries:Ohio series (1883-1890)]

[:ElPasoBaseLine:El Paso base line (1879)]

[:IndianaSeries:Indiana series (1879-1890)]

[:YoloBaseLine:Yolo base line (1881)]

[:IllinoisSeries:Illinois series (1871-1883)]

[:HoltonBaseLine:Holton base line (1891)]

[:MissouriSeries:Missouri series (1871-1880)]

[:StAlbansBaseLine:St. Albans base line (1892)]

[:MissouriKansasSeries:Missouri-Kansas series (1880-1890)]

[:SalineBaseLine:Salina base line (1896)]

[:KansasColoradoSeries:Kansas-Colorado series (1880-1881, 1891-1893)]

[:SaltLakeBaseLine:Salt Lake base line (1896)]

[:RockyMountainSeries:Rocky Mountain series (1879-1880, 1885-1985)]

[:VersaillesBaseLine:Versailles base line (1897)]

[:NevadaSeries:Nevada series (1876, 1879-1892)]

[:WesternSeries:Western or coast range series (1876, 1878, 1880-1884, 1891-1892)]

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