<Tr> <Th> March 1, 1977 </Th> <Td> The United States claimed maritime borders west of the Strait of Juan de Fuca, within the Dixon Entrance, and in the Beaufort Sea that conflicted with claims of Canada . </Td> <Td> no change to map </Td> </Tr> <Tr> <Th> May 26, 1977 </Th> <Td> Several parcels were exchanged between Texas and Mexico along the Rio Grande in areas near Presidio and Hidalgo, Texas, including the Horcón Tract, on which the town of Río Rico was located, and Beaver Island near Roma, Texas . In addition, Mexico ceded 823 acres (3.33 km) to the U.S., while the U.S. ceded 2,177 acres (8.81 km) to Mexico, primarily to straighten sections of the Rio Grande for flood control . </Td> <Td> </Td> </Tr> <Tr> <Th> October 1, 1978 </Th> <Td> Tuvalu became independent from the United Kingdom . It claimed the atolls of Funafuti, Nukufetau, Nukulaelae, and Niulakita . </Td> <Td> Pacific Ocean: </Td> </Tr> <Tr> <Th> July 12, 1979 </Th> <Td> The Republic of Kiribati became independent from the United Kingdom . It claimed Birnie Island, Canton Island, Caroline Island, Christmas Island, Enderbury Island, Flint Island, Gardner Island, Hull Island, Malden Island, McKean Island, Phoenix Island, Starbuck Island, Sydney Island, and Vostok Island . This dissolved the condominium of the Canton and Enderbury Islands . </Td> <Td> Pacific Ocean: </Td> </Tr>

What was the western boundary of the united states