The Columbia River was the artery.

Everything moved along it: furs going west toward the coast and eventually toward China or Europe, trade goods going east toward the interior posts, personnel moving in both directions throughout the year.

The timing of this movement was predictable: spring and fall were the primary seasons of travel, when the river was navigable and the weather was sufficiently moderate to make long-distance canoe travel feasible.

The posts along the river and its tributaries were nodes in this network: Fort Astoria at the mouth, Fort Nez Perce (originally Fort Walla Walla) at the confluence of the Walla Walla and Columbia, Fort Okanogan to the north in present-day Washington.