Base No. 6
Did you know? There’s a perfectly straight line on Edisto Island, nearly seven miles long that runs from Edisto Beach State Park to the DNR’s Botany Bay Plantation Heritage Preserve. We know this because two granite obelisks mark the line’s beginning and end points, and the obelisks themselves sit atop massive granite blocks buried 3 feet beneath the ground, with a copper pin embedded in each denoting the precise beginning and end of this meticulously surveyed line.
All of this may sound terribly mysterious, but lay your notions of ancient civilizations and alien visitors aside. In fact, the line and the markers are artifacts of the much more recent past, 1849 to be exact. Though the technology used to create the line was, at the time, at the vanguard of scientific achievement in the field of mapmaking. Base Number 6 and other similar lines were surveyed along the eastern coast of the then-young United States of America to facilitate the creation of more accurate nautical maps for shipping and commerce.
The “U.S. Coast Survey” project was approved by President Thomas Jefferson and carried out beginning in the early 1800s. Measuring and marking “baselines” of known length allowed mapmakers of the period to create accurate charts through the process of “triangulation.” The endpoint markers for “Baseline Number 6,” surveyed across Edisto in 1849 under the supervision of Alexander Bache, great-grandson of Benjamin Franklin and the second Superintendent of the Coast Survey (today a part of the National Oceanic and Atmospheric Administration) are now a part of the National Register of Historic places. Given the technology available to the surveyors and scientists, the laying out of the Edisto baseline and the other baselines that formed the basis for mapping the coast of the U.S. was a remarkable achievement. The line, which was measured using an enormous pair of metal bars that had to be laid end-to-end over and over again by workers along the route of the survey, was measured using modern GPS technology and found to be accurate to 2.5” inches. Truly a remarkable achievement.
The survey’s easternmost marker can be seen at the Edisto State Park Education Center, where the DNR Board recently held its monthly meeting. The Western-end marker can be found just about seven miles away as the crow flies (assuming a crow that can fly a REALLY straight line), at the DNR’s Botany Bay Plantation Heritage Preserve and Wildlife Management Area, one of many treasures preserved for visitors to that property.