WAWashington Geography

The Hoh Rain Forest, on the west side of the Olympic Peninsula, collects somewhere between 140 and 170 inches of rain in an ordinary year. Sequim sits about 60 miles away on the northeast corner of the same peninsula, takes in roughly 16 inches, and grows lavender commercially. Nothing stands between them except the Olympic Mountains, which wring the Pacific storms out on the way over. No statewide average survives contact with that fact.

One mountain wall, two Washingtons

The Cascade Range runs the full height of the state from the Canadian border down to the Columbia River, and it separates two places that share a legislature and almost nothing else. West of the crest: Douglas fir, moss, Puget Sound, ferries, Seattle. East of it: sagebrush steppe, irrigated orchards, dryland wheat, Spokane. Yakima lies about 100 miles from Seattle and averages under nine inches of precipitation a year.

That crest is a volcanic arc, built where the Juan de Fuca plate slides beneath North America a hundred miles offshore. Five stratovolcanoes stand along it in Washington: Mount Baker, Glacier Peak, Mount Rainier, Mount Adams and Mount St. Helens.

Rainier is a mountain made largely of ice

At 14,411 feet, Mount Rainier is the state's high point and carries around 26 named glaciers, more ice than all the other Cascade volcanoes combined. The Carbon Glacier on the north side reaches down to roughly 3,500 feet, the lowest glacier terminus in the contiguous United States, and is the thickest by depth. Emergency planners in Tacoma and the Puyallup valley worry less about lava than about lahars, slurries of melted ice, ash and loose rock that have run all the way to Puget Sound in the past and would follow the same valleys again.

Mount St. Helens demonstrated the range's temper on May 18, 1980. The north flank slid away in the largest debris avalanche ever recorded, the lateral blast flattened forest across roughly 230 square miles, and the summit dropped from 9,677 feet to 8,363 feet in a morning. Spirit Lake was buried, then re-formed about 200 feet higher than it had sat before, with a raft of dead trees still floating on it.

The dry half was carved by floods, not rivers

Eastern Washington's scablands are out of proportion to the water in them: coulees hundreds of feet deep with dry floors, potholes scoured into basalt, gravel bars the size of hills. J Harlen Bretz argued from the 1920s that catastrophic floods had cut them and spent decades being told this was impossible. He was right. Glacial Lake Missoula, held in place by an ice dam in Idaho, burst dozens of times between roughly 15,000 and 13,000 years ago and sent walls of water across the Columbia Plateau.

Dry Falls near Coulee City is the fossil of the largest of those cataracts, a cliff about 3.5 miles wide and 400 feet high with nothing going over it. Grand Coulee above it now holds Banks Lake. Where the water did not scour, wind piled loess into the dunes of the Palouse, deep silt that has grown wheat since the 1880s. Under all of it lies the Columbia River Basalt Group, lava that erupted between about 17 and 6 million years ago and stacked thousands of feet thick.

Borders set by treaty, by arbitration, and by a shot pig

The northern boundary is the 49th parallel, fixed by the Oregon Treaty of 1846. The treaty then sent the line through the middle of the channel to the sea without saying which channel. Britain read that as Rosario Strait, the United States as Haro Strait, and the San Juan Islands sat in the gap between the two readings. In 1859 an American settler shot a British pig on San Juan Island. Both sides landed troops, nobody else was killed, and the two nations kept rival military camps on the island for twelve years until Kaiser Wilhelm I, acting as arbitrator, ruled for the Haro Strait line in 1872.

That same parallel clips the bottom of the Tsawwassen peninsula, leaving Point Roberts as about five square miles of Washington reachable by land only through British Columbia. Its teenagers cross an international border twice in each direction to attend high school in Blaine.

The southern boundary follows the Columbia River for roughly 300 miles, then leaves the water near Wallula and runs east along the 46th parallel to Idaho. The Columbia is the only river that cuts clean through the Cascade Range at sea level, which is why the highway, the railway and the barge traffic all share the Gorge.

Records at both ends of the scale

The state high is 120 degrees at Hanford on June 29, 2021, during the Pacific Northwest heat dome. The low is 48 below zero at Mazama and Winthrop, neighbouring towns in the Methow Valley, on December 30, 1968.

Snow is where Washington holds a world record. The Mount Baker Ski Area measured 1,140 inches in the winter of 1998 to 1999, the most ever recorded in a single season anywhere on earth. It took the title from Paradise on Mount Rainier, which had piled up 1,122 inches in 1971 to 1972.

The whole state keeps Pacific Time. Puget Sound, a fjord system gouged by the Puget lobe of the ice sheet and flooded when it melted, gives Washington roughly 3,000 miles of tidal shoreline against about 157 miles of open Pacific coast.

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