been dammed by the Umatilla Highlands. This huge lake now had its Eastern border at the Umatilla Highlands and its Western border at the Cascade Range. The fighting did not cease, and ultimately, the enormous Cascade Mountains were breached, and the water that had accumulated raced to the sea, creating the Columbia River Estuary. Thus the “Great Water” assumed the flow that it follows today, and Speelyei finally killed Wishpoosh out in the open ocean; his body washed up south of the Estuary. Colonisation After colonisation, the Chinookans signed a treaty with Anson Dart in 1851 to grant their people the right to stay on their traditional lands at the Estuary rather than be moved to a reservation east of the Cascade Range. However, the US congress never ratified the treaty, resulting in conflicts and a string of legal battles that began in 1899 and have continued to the present day. Discovery In 1788 a fur trader named John Meares came within kilometres of discovering the Estuary; however, his ship could not navigate the rough breakers at the bar, and he ended up deciding that there was not a river behind it at all. He did name the Northern point Cape Disappointment (Chinookan: kah’see). In 1792, Robert Gray, an American fur trader, crossed the bar in his ship the Columbia Redeviva and became the first white settler to enter the estuary, subsequently naming the estuary Gray's Bay and the river Columbia River. During the 20th century, there existed some ambiguity with regards to who discovered the estuary, though today it is unequivocally considered to be Gray. Geology The Columbia River Estuary is in a valley that has been cut into marine sediments and volcanic rocks from the Tertiary period. The estuary receives large volumes of water from the Cascade Range, mountains to its east that trap precipitation and moisture. Pleistocene and Holocene sediments have filled the valley and continue to do so, dominating the estuary's morphology. Plate Tectonics The estuary is part of the North American plate and sits on an active continental margin. The Juan de Fuca plate is subducting underneath it and has resulted in eruptions of andesitic volcanoes in the Cascade Range (See: Mt St Helens). Additionally, tilting of the continental crust has occurred, resulting in the coastal region around the estuary being uplifted and some of Washington and Oregon's interior regions being downwarped along a trough.