Boundary disputes

Initial formal claims to the region were asserted by Spain in 1513 with explorer Nuñez de Balboa, the first European to sight the Pacific Ocean from the Americas. Russian Maritime Fur Trade activity, through the Russian-America Company, extended from the farther side of the Pacific to Russian America. This prompted Spain to send expeditions north to assert Spanish ownership, while Captain James Cook and subsequent expeditions by George Vancouver advanced British claims. As of the Nootka Conventions, the last in 1794, Spain gave up its exclusive a priori claims and agreed to share the region with the other Powers, giving up its garrison at Nootka Sound in the process.
The United States established a claim based on the discoveries of Robert Gray, the Lewis and Clark Expedition, the construction of Fort Astoria, and the acquisition of Spanish claims given to the United States in the Adams–Onís Treaty.^[30] From the 1810s until the 1840s, modern-day Washington, Oregon, Idaho, and western Montana, along with most of British Columbia, were part of what the United States called the Oregon Country and Britain called the Columbia District. This region was jointly claimed by the United States and Great Britain after the Treaty of 1818, which established a co-dominion of interests in the region in lieu of a settlement. In 1840 American Charles Wilkes explored in the area. John McLoughlin, Chief Factor of the Hudson's Bay Company, headquartered at Fort Vancouver, was the de facto local political authority for most of this time.
This arrangement ended as U.S. settlement grew and President James K. Polk was elected on a platform of calling for annexation of the entire Oregon Country and of Texas. After his election, supporters coined the famous slogan "Fifty-four Forty or Fight", referring to 54°40' north latitude—the northward limit of the United States' claim.^[31] After a war scare with the United Kingdom, the Oregon boundary dispute was settled in the 1846 Oregon Treaty, partitioning the region along the 49th parallel and resolving most but not all of the border disputes (see Pig War).
The mainland territory north of the 49th parallel remained unincorporated until 1858, when a mass influx of Americans and others during the Fraser Canyon Gold Rush forced the hand of Colony of Vancouver Island's Governor James Douglas, who declared the mainland a Crown Colony. The two colonies were amalgamated in 1866 to cut costs, and joined the Dominion of Canada in 1871. The U.S. portion became the Oregon Territory in 1848. It was later subdivided into Oregon Territory and Washington Territory. These territories became the states of Oregon, Idaho, Washington and parts of other Western states.
American expansionist pressure on British Columbia persisted after the colony became a province of Canada, even though Americans living in the province did not harbor annexationist inclinations. The Fenian Brotherhood openly organized and drilled in Washington, particularly in the 1870s and the 1880s, though no cross-border attacks were experienced. During the Alaska Boundary Dispute, U.S. President Teddy Roosevelt threatened to invade and annex British Columbia if Britain would not yield on the question of the Yukon ports. In more recent times, during the so-called "Salmon War" of the 1990s, Washington Senator Slade Gorton called for the U.S. Navy to "force" the Inside Passage, even though it is not an official international waterway. Disputes between British Columbia and Alaska over the Dixon Entrance of the Hecate Strait between Prince Rupert and Haida Gwaii have not been resolved.^[32]

Geology

Further information: Geology of the Pacific Northwest

The Northwest is still highly geologically active, with both active volcanoes and geologic faults.^[33]
Active volcanoes in the region include Mount Garibaldi, Mount Baker, Mount Rainier, Mount Saint Helens, Mount Hood, Mount Jefferson, and Mount Shasta.