Gold on the Thompson and Fraser rivers emptied California northward in the spring of 1858. Within a month, 30,000 men descended on Victoria, a town of roughly 500 people - among them some 4,000 Chinese miners, alongside Americans, Britons, Germans, Hawaiians, Mexicans, West Indians, and French Canadians. Governor James Douglas responded with a rule: entry to the goldfields must be made through Victoria, and from there up the Fraser by water. The rule had teeth and reasons behind it. It let officials strip incoming Americans of handguns, and it protected the Hudson's Bay Company's still-intact monopoly on trade with Indigenous nations. It also meant tolls, licences, and a British hand on every arrival. Douglas was trying to keep a colony from being invaded by its own gold rush.

Americans looked at a map and found a way around him. The trail started at Bellingham Bay, at Fairhaven, now a neighbourhood of Bellingham, and ran inland and north. It could not take the obvious line - the modern border crossing at Sumas - because Sumas Lake lay in the way, a shallow sheet of some 4,000 hectares spreading across the lowland. So the route swung east through the Columbia Valley, a lowland corridor linking the mid-Nooksack River country with Cultus Lake and the lower Chilliwack River, emerging in the upper Fraser Valley about 80 kilometres east of present-day Vancouver. A second option, the Skagit Trail, climbed the Skagit River to its headwaters and dropped into the Fraser near the Hudson's Bay post at Fort Hope. No one counted the travellers on either route. Thousands is the safe word.

Boomtowns build in canvas and green lumber, which is why almost nothing from 1858 survives on Bellingham Bay. One thing does. That year Thomas G. Richards and his brother Charles put up a store to outfit men heading for the trail, spending $8,000 on a building whose bricks came by sea from San Francisco aboard the bark Ann Parry. It is the oldest brick building in Washington. The gold rush collapsed almost as fast as it arrived, and the store went on to other lives, eventually serving as a territorial courthouse. It was added to the National Register of Historic Places in 2003, restored to its period appearance in 2020, and reopened the following year as the Helen Loggie Museum of Art at 1308 E Street - a merchant's speculation on a stampede, still standing long after the stampede was forgotten.

The trail's real significance was what it proved: the young colony could not stop Americans from walking in. United States troops of the Border Commission, stationed near the trail's southern end, went on alert during the McGowan's War standoff in the Fraser Canyon and again during the San Juan Islands dispute - the confrontation remembered, almost fondly now, as the Pig War. The nervousness ran both directions. On the Canadian side, a large tract at Sardis was set aside as a military reserve during the Fenian raid scares of the 1870s and 1880s, land that would later become Canadian Forces Base Chilliwack. That reservation was aimed less at American aggression than at the Stó:lō, whose numbers in the valley the colonial authorities found unsettling, and on whose territory the garrison sat.

The word Whatcom comes from the Lummi place name x̣ʷátqʷəm, probably meaning "noisy," a reference to a waterfall. The lake that forced the trail east is gone: between 1920 and 1924, engineers diverted the Chilliwack River into the Vedder Canal and drained Sumas Lake into farmland, taking with it a fishery and a way of life the Semá:th people had built around it. The lake has not entirely accepted the verdict. In November 2021, floodwater filled the old basin again, drowning a highway and forcing more than a thousand households from their homes. For a few days the obstacle that shaped the Whatcom Trail was back where it had always been.