For emphasis.............the area west of the DC monument.........is man made..................then u have the Potomac river.............and then VA........

After a disastrous flood in 1881, the United States Army Corps of Engineers dredged a deep channel in the Potomac and used the material to fill in the Potomac (creating the current banks of the river) and raise much of the land near the White House and along Pennsylvania Avenue NW by nearly 6 feet (1.8 m).^[7][8][9] Much of the dredged material was used to build up the existing tidal flats in the Potomac River as well as sandbars which had been created by silting around Long Bridge.^[10]Reclamation occurred in three phases: Section 1 (what is now 135-acre (550,000 m²) West Potomac Park), section 2 (what is now the 277-acre (1,120,000 m²) area around the Tidal Basin), and section 3 (what is now 327-acre (1,320,000 m²) East Potomac Park).^[11] Congress formally designated these areas "Potomac Park" on March 3, 1897.^[12]

To ensure that the island was not eroded by the river, poplars and willows were planted along edge of the island to stabilize the shoreline.^[13] Over the next two decades, most of East Potomac Park lay untouched, and dense thickets of trees and brush grew up on the island.^[14] Dredging of the Potomac River continued even after East Potomac Park was considered finished, and additional dredged material was placed on the island in late 1900,^[15] 1901, 1902,^[16] 1903,^[17] 1904,^[18] and 1907.^[19]