The datum is defined by the observed heights of mean sea level at the 26 tide gauges and by the set of elevations of all bench marks resulting from the adjustment. A total of 106,724 kilometers of leveling was involved, constituting 246 closed circuits and 25 circuits at sea level.
George Washingtonâs Mount Vernon is located roughly 15 miles south of Washington, D.C. and 8 miles south of Alexandria, Virginia on the banks of the Potomac River, at the southern end of the George Washington Memorial Parkway.
It is 18% greater than the overall U.S. average. On 5/31/1985, a category F3 (max. wind speeds 158-206 mph) tornado 19.9 miles away from the Mount Vernon city center killed one person and injured 20 people and caused between $5,000,000 and $50,000,000 in damages.