The Convention of 1818 (Convention of Commerce), 20 October 1818, described the boundary between British North America and the US as a line from the farthest northwest point of Lake of the Woods "north or south, as the case may be" to the 49th parallel and thence west along the parallel to the "Stony" [Rocky] Mountains. The area west of the Rocky Mts was to be "free and open" to either Britain or the US for the next 10 years. In 1827 this period was indefinitely extended, but it was ultimately terminated by the 1846 OREGON TREATY.