Colorado: the state was drawn with a ruler, and almost everyone lives along a single line

01 A rectangle drawn in Washington

On 28 February 1861 the United States Congress created the Colorado Territory with a text that names neither a river nor a mountain: two parallels, 37 and 41 north, and two meridians counted from Washington, equivalent to 102 and 109 west of Greenwich. The borders have not changed since. Land was taken from four neighbouring territories (Kansas, Nebraska, Utah and New Mexico) and every feature of the terrain was left out: the Continental Divide crosses the state through the middle, the Colorado River leaves through the west and the Great Plains come in through the east without the line flinching.

That abstraction has an epilogue that people here like to tell. The surveyors who turned paper into boundary markers, from 1879 onwards, worked with magnetic compasses and metal chains over unforgiving ground, and the line wandered at hundreds of points; by one count made on present-day mapping, the "rectangle" has 697 sides. In the south-west corner, the Four Corners Monument, the only point in the country where four states touch, stands some 550 metres from the spot the law specified, and the courts ruled that the border is where the marker is, not where the text said. It is a small detail, but it says something about the place: Colorado began as an idea drawn from far away and then had to be fitted to the ground.

02 The three Colorados that fit inside

If you enter from Kansas on Interstate 70, Colorado does not look like Colorado for almost three hours. The eastern two-fifths of the state are Great Plains: wheat, grassland, grain elevators, one-street towns with the name painted on the water tower. The state's lowest point is here, where the Arikaree River leaves for Kansas at 1,011 metres, and even so it is the highest low point of any state in the country, above the highest summit of eighteen states. In other words, the "flat" part of Colorado is already higher than almost all of the eastern United States.

Then a blue line appears on the horizon, does not move for an hour, and suddenly becomes a wall. That is where the second Colorado begins: the mountains, with 58 summits above 4,267 metres and a mean elevation for the state of around 2,070 metres, the highest in the country. And on the other side of the Continental Divide is the third: the Western Slope, mesas, red sandstone canyons and irrigated valleys where peaches and vines grow, with a climate closer to Utah's Great Basin than to Denver's. Grand Junction, its main city, has some 72,000 residents and sits about 390 kilometres and four hours from the capital along a highway that snow or a rockfall in Glenwood Canyon closes from time to time.

The population figures tell the real story. The plains cover around 40 per cent of the territory and hold about 2 per cent of the people; in 1920 they held 17 per cent. The Western Slope accounts for around 11 or 12 per cent. Everyone else, between 84 and 85 per cent of nearly six million residents, lives in a strip some 300 kilometres long and a few dozen wide pressed against the foot of the mountains, from Fort Collins to Pueblo by way of Boulder, Denver and Colorado Springs. The rectangle has three landscapes; the people live on the edge between two of them.

03 The seam: where the plains hit the mountains

What makes that strip strange is that it is not a transition. In many ranges the plain rises gradually: hills, then foothills, then mountains. On Colorado's Front Range there are almost no steps: the plain arrives at around 1,600 metres and the range rises at once to more than 4,000 within about thirty kilometres. The first obstacle is a narrow ridge of tilted sandstone, the Dakota Hogback, which runs north to south like a spine and which the roads cross through the few gaps cut by streams. In Boulder the same geology surfaces as the Flatirons, slabs of reddish rock leaning against the mountain, a little over two kilometres from downtown.

Denver was founded in 1858 right on that seam, where Cherry Creek joins the South Platte, and its old nickname says it plainly: "Queen City of the Plains". It is not a mountain city, even though visitors arrive expecting one: it is a city of the plains that faces the mountains. The same is true of Colorado Springs, Fort Collins and Pueblo. All of them sit on the flat side of the line, at exactly the height where a grid can still be laid out and, at the same time, the range stands at the end of every street that runs west.

04 The mountains are the compass

Living on that seam produces a habit that strikes anyone arriving from elsewhere: almost nobody here uses the points of the compass; they use the mountains. "Towards the mountains" is west; "away from the mountains" is east; and that is how directions are given, how people park and how they choose a side of the road. In the lists of jokes about how to recognise someone from Colorado the same one always appears: they have a sense of direction that works in only two directions, towards the mountains and away from them, and they get lost in any city where the range is not where it should be.

That reflex has quiet consequences. In the Front Range strip the western wall can be seen from almost anywhere, changes colour with the hour and keeps snow for much of the year, so it works as a clock and as a weather forecast: local people look that way before deciding what to do with the afternoon. Those who live on the Western Slope, by contrast, say it with some resignation: there the mountains lie in several directions and the trick does not work. It is another way of saying that the seam is the centre of the state and everything else the sides.

05 The east that is emptying out

The plains are the part of Colorado that appears least on postcards and explains most about how it is lived. Many eastern counties reached their peak population in 1920 or 1930 and have been losing people ever since: the plains as a whole lost almost 14,000 residents between 1920 and 1940 and kept falling, more slowly, until the end of the century. Baca County, in the south-east corner, had 10,570 residents in 1930; the dust storms of that decade took away more than four thousand, and in 2020 there were 3,506 left. Part of the abandoned land was bought by the federal government and is now the Comanche National Grassland, where the ruts of nineteenth-century wagons can still be made out in the grass.

This explains a contrast you feel while travelling: two hours from the densest part of the state lies a territory the size of a European country with little more than one inhabitant per square kilometre, where the silence is not scenery but consequence. And it explains, in reverse, why the strip at the foot of the mountains grew so much: the people of the plains, for the most part, did not leave for another state; they moved to the edge. Between 2023 and 2024, 92 per cent of Colorado's population growth took place in the Front Range counties. The rectangle empties on one side and fills along a line.

06 The other side of the Divide

Crossing to the west is changing country without changing state. Past the Eisenhower Tunnel, at around 3,400 metres, the interstate drops down the valley of the Colorado River into a landscape of red sandstone, canyons and mesas: Colorado National Monument, the Grand Mesa, the Book Cliffs. The Grand Junction valley lies at around 1,400 metres, and at Palisade, at its eastern end, the air flowing down from De Beque Canyon keeps the nights warm enough for peaches to grow at that altitude, with a growing season of around 180 days. Irrigation canals from 1913 onwards turned a dry valley floor into orchards.

What you notice on arrival is not only the geology but the scale and the tone. The largest city is the size of a Denver district, journeys are measured in hours rather than minutes, and when someone here talks about "the Front Range" it is as another place. Even the region's name is vague: there is no official line saying where the Western Slope begins; a geographer consulted by the state's public radio described it as more a sense of belonging to a community than a boundary. Living here is living in Colorado without living on the seam, and that difference weighs more than the kilometres.

07 A state of newcomers

One last piece is needed to understand the strip. Colorado's population is not only concentrated; it is also, for the most part, from elsewhere. According to census estimates for 2024, some 2.4 million of the 5.96 million residents were born in the state: 41 per cent. Six out of ten people you pass on a street in Denver or Boulder came from somewhere else. That is nothing new: the state began that way, with a gold rush in 1858 and 1859 that brought tens of thousands of people to the foot of the mountains in a couple of summers, and Denver was born as the camp of that arrival.

A place where most people have just arrived and almost everyone lives on the same edge produces a recognisable culture: little attachment to the old, a great deal of conversation about what to do outdoors at the weekend and a relationship with the mountains that is more about use than inheritance. The rectangle was drawn by someone who had never been here; the people who inhabit it, for the most part, were not born here either. Colorado is a state you arrive in, and the mountains are what everyone looks at while they settle.

08 What a few days here feel like

The first days are organised by the line in the west. You catch yourself looking for it as you leave any building, using the mountains to know where you are, watching the clouds pile up over the summits after lunch. You learn that the city is on the plain and the mountains are forty minutes away, and that that journey, from asphalt to tundra, is what people here make every weekend.

Then, if you leave the strip, the state comes apart into its three pieces. To the east, grass, sky and towns with more history than inhabitants. To the west, past the tunnel, another light and another rock. You understand that the straight line on the map has nothing to do with what lies inside it, and that what they call Colorado is really a three-hundred-kilometre seam between two worlds, one emptying out and the other far away.

What tends to stay in the memory is no particular summit. It is the blue wall seen from the plain, always on the same side, and the sense that everyone here, born or newly arrived, is oriented towards it.