Snoqualmie Pass: The I-90 Corridor and the Mountain Pass That America Drives Through

Every truck carrying goods from the Pacific ports to the interior of the continent drives through Snoqualmie Pass. Every car making the trip between Seattle and eastern Washington and the rest of the country crosses here, at about three thousand fifteen feet, where Interstate Ninety cuts through the Cascades at the lowest available crossing.

The pass has been a transportation corridor for thousands of years. The Snoqualmie and Yakama peoples crossed here seasonally, following the berry harvests and hunting grounds on opposite sides of the range. The first wagon road through the pass was completed in eighteen sixty-seven. The Northern Pacific Railroad considered and rejected it in favor of a lower route further south.

What makes Snoqualmie Pass notable now is not just the traffic. The Mount Baker-Snoqualmie National Forest surrounds the corridor on both sides, and within that corridor, researchers at the University of Washington have been monitoring snowpack, precipitation, and streamflow for decades. The South Fork Snoqualmie watershed is one of the most-studied hydrological systems in the Pacific Northwest, partly because it is so accessible and partly because it supplies drinking water to the city of Seattle.

The corridor is also the subject of one of the most ambitious wildlife crossing projects in the country. The Interstate Ninety Wildlife Bridges project, a collaboration among the Washington Department of Transportation, the Forest Service, and several tribal nations, has been building a series of over-highway and under-highway passages that allow black bears, elk, mountain lions, and other species to cross the highway without being killed. The Cascades have been bisected by this road for seventy years. The crossings are an attempt to reconnect what the road divided.