From Fort Chipewyan, Mackenzie and his companians traveled west up the Peace River and its tributary the Parsnip River. As they traveled, they were essentially handed from one native tribe to the next, usually quite peaceably and without much incident. After crossing the Continental Divide, Mackenzie discovered the Fraser River, which he mistakenly took to be the headwaters of the Columbia River, which had been named and partially explored from the Pacific by Captain Robert Gray of Boston in the ship Columbia in 1790.
Mackenzie and his party left the Fraser River, traveled along the course of the Blackwater River, and then proceeded overland due west. After crossing the Coastal Range, they descended the Bella Coola River in a borrowed dugout canoe to arrive at a tidal inlet near the present-day village of Bella Coola. As they neared the coast, the natives, with obvious experience from previous contact with Europeans, behaved in a decidedly more acquisitive and temperamental fashion. About twenty miles west of present-day Bella Coola, British Columbia, Mackenzie tasted salt water and wrote in vermilion paint on a rock just above the high-tide line the inscription: Alex Mackenzie from Canada by land 22 d July 1793. Somewhat embellished with carved lettering and white paint over the years, the original inscription is still visible today. Thus, Mackenzie became the first European to cross the continent from ocean to ocean north of Mexico.
Mackenzie’s journey to the Pacific in 1793 and his supposed but mistaken discovery of the headwaters of the Columbia River provided powerful support to the British claim over the entire Pacific Northwest, including present-day Washington and Oregon. It also generated an equally strong desire by Thomas Jefferson to counter the British claim with an American expedition overland to the Pacific. Mackenzie’s expedition and discovery, coming after Cook’s and Vancouver’s monumental exploratory expeditions, was a major stimulus to Jefferson’s decision to commission the Lewis and Clark Expedition of 1803–1805.