A few members of the Corps of Discovery crossed the continental divide at Lemhi Pass on the present-day Montana-Idaho border in mid-August 1805. At that moment, they became the first minuscule trickle in what would become a Noah-style deluge of humanity pouring across North America’s mighty spine, rushing headlong toward the rich lands along the Pacific.

Geologists tell a fascinating, frightening tale of cataclysmic prehistoric floods unleashed down the Columbia as vast volumes of glacier water were freed time after time by immense decaying ice dams high in the mountains. In its way, the great migration of people set off by Lewis and Clark is the anthropological equivalent of these tremendous ice age floods. Sweeping aside all but the hardiest Native American survivors, a quickening torrent of settlers became like raindrops that spatter down in the mountains, collecting and growing and speeding their way down to the sea.

Consider this: 200 years ago this week, the 33-member Lewis and Clark Expedition made camp just across the Columbia within easy sight of modern Astoria, the only people of European descent in all of what only 84 years later would become Washington state. Last week, in what it called a conservative forecast, a state agency said Washington can expect 33 new permanent residents to arrive every three hours over the course of the next decade.

The mere fact the earth has swept around the sun 200 times is a thin pretext to set this year apart from all others to ponder the achievements and consequences of this small band of adventurers, with their rain-rotted animal-hide clothing and cheap blue trade beads. Were it not for our culture’s fascination with years that end in zero, we could as easily mark the expedition’s 222nd anniversary, or the 75,000th day since they managed to light their first soggy fire on the Columbia estuary.

Of all the many abstractions symbolized by Lewis and Clark, change is the most potent. The Corps of Discovery represents a spark, a fulcrum, a catalyst in the ever-accelerating story of humanity. By deliberately conspiring to consider 200 years to be a meaningful historical milestone, we provide ourselves with a kind of punctuation mark – a comma perhaps – in the relentless yet inspiring triumph of what we flatter ourselves to call civilization.

This Bicentennial will soon pass. But inspired by the courage and fortitude of these genuinely brave people, we should endeavor to live our lives not as a rushing flood, but as individuals who study our surroundings with care and pause to learn from all those we meet along the way.