 In reality, the river originates some 1,000 miles to the north and east in Canada, but it would be 18 years later before the entire river was charted by another famed British explorer named David Thompson.Captain Gray's discovery of the Columbia opened trade between Europeans and Chinook Indians who lived along the lower Columbia between the Cascade region and the river's mouth.U.S., British, Spanish and Russian fur traders bartered for sea otter and beaver skins in the late 18th century.