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The first European record of a landing on the Washington coast was in 1774 by Spaniard Juan Pérez. One year later, Spanish Captain Don Bruna de Heceta on board the Santiago, part of a two-ship flotilla with the Sonora, landed near the mouth of the Quinault River and claimed the coastal lands up to the Russian possessions in the north.

In 1778, the British explorer Captain James Cook sighted Cape Flattery, at the entrance to the Strait of Juan de Fuca. But the strait itself was not found until Charles William Barkley, captain of the Imperial Eagle, sighted it in 1787. Barkley named it for Juan de Fuca. The Spanish-British Nootka Conventions of the 1790s ended Spanish exclusivity and opened the Northwest Coast to explorers and traders from other nations, most important being Britain, Russia, and the United States. Further explorations of the straits were performed by Spanish explorers Manuel Quimper in 1790 and Francisco de Eliza in 1791 and then by British Captain George Vancouver in 1792. Captain Vancouver claimed the sound for Britain and named the waters south of the Tacoma Narrows Puget's Sound, in honor of Peter Puget, who was the lieutenant accompanying him on the Vancouver Expedition. The name later came to be used for the waters north of Tacoma Narrows as well.[5] Vancouver and his expedition mapped the coast of Washington from 1792 to 1794.[6]

Captain Robert Gray (for whom Grays Harbor County is named) discovered the mouth of the Columbia River in 1792, naming the river after his ship "Columbia" and later establishing a trade in sea otter pelts. The Lewis and Clark expedition, under the direction of President Thomas Jefferson, entered the state from the east on October 10, 1805. Meriwether Lewis and William Clark were surprised by the differences in Indian tribes in the Pacific Northwest from those they had encountered earlier in the expedition, noting, in particular, the increased status of women among both coastal and plateau tribes. Lewis hypothesized that the equality of women and the elderly with men was linked to more evenly distributed economic roles.

Canadian explorer David Thompson extensively explored the Columbia River commencing in 1807. In 1811, he became the first European to navigate the entire length of the river to the Pacific. Along the way he posted a notice where it joins the Snake River claiming the land for Britain and stating the intention of the North West Company to build a fort there. Subsequently, Fort Nez Perces trading post, was established near present-day Walla Walla, Washington. Thompson's notice was found by Astorians looking to establish an inland fur post. It contributed to David Stuart's choice, on behalf of the American Pacific Fur Company, of a more northerly site for their operations at Fort Okanogan.

By the time settlers arrived in the 1830s, a population of Métis (mixed race) people had grown from centuries of early-European fur traders procreating with Native American women.[7] Before Caucasian women began moving to the territory in the 1830s, it was not uncommon for traders to seek Métis women for wives.

American–British occupation disputes

Main article: Oregon boundary dispute

American interests in the region grew as part of the concept of manifest destiny. Spain ceded their rights north of the 42nd Parallel to the United States by the 1819 Adams-Onís Treaty, (but not possession, which was disallowed by the terms of the Nootka Conventions).

Britain had long-standing commercial interests through the Hudson's Bay Company and a well-established network of fur trading forts along the Columbia River in what it called Columbia District. These were headquartered from Fort Vancouver in present-day Vancouver, Washington.

By the Treaty of 1818, following from the War of 1812, Great Britain and the United States established the 49th parallel as the border west to the Continental Divide of the Rocky mountains; but agreed to joint control and occupancy of Oregon Country. In 1824, Russia signed an agreement with the U.S. acknowledging it had no claims south of 54-40 latitude north and Russia signed a similar treaty with Britain in 1825.