On the surface, the two states appear to have much in common. They share a border, a birth month (July 1890) and even — for a few brief heady months in 1863 — membership in the “Idaho Territory.”

So why are so many people leaving Wyoming while Idaho booms?

For clues, look at the full ranking. The Pacific Northwest and Mountain West are extremely well represented at the top of the chart...

...but Wyoming and West Virginia are stuck to the bottom. Those two, and others in the lower echelon, have something in common: resource dependence. In their case, it’s primarily coal mining.

Wyoming has long been the nation’s coal king. The vast operations of the Powder River Basin produce more coal than all but a handful of states put together. But cheap natural gas has reduced power plants’ dependence on the mineral and, with it, its price and production. Wyoming’s mines are shipping out fewer tons of coal and getting paid less for each of them.

That helps explain why the state went from the fourth-fastest growing in 2012 (D.C. was first that year) to rock bottom in 2017.

Idaho, meanwhile, produces no coal to speak of, and has no significant petroleum or natural-gas reserves, according to the Department of Energy. There’s some mining activity in the state, but it’s small compared to neighbors such as Utah, Nevada and Wyoming.

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It wasn’t always so. Gold rushes, starting in the Civil War era, were a defining feature of the Idaho Territory’s early economy. In 1900, 10 years into each state’s history, mining made up as much of Idaho’s employment base as it did Wyoming’s. But in the century to follow, Idaho’s mineral wealth ran low and it was forced to diversify, while the Cowboy State would double down on coal.

That’s given Wyoming a powerful coal industry and median incomes far above Idaho’s, but it has also put the state’s economy at the mercy of the boom-and-bust cycles that characterize the global commodity market and sapped incentive to build up a more robust local economy.

Like Alaska and West Virginia, which also lost population in 2017, Wyoming is suffering from a tamer version of the “resource curse,” in which natural-resource wealth actually harms developing countries because it crowds out important long-term investments in infrastructure, education and industrialization.

Resource-dependent states may see a population recovery in 2018 thanks to a partial recovery in energy prices, but that does nothing to break their cycle of dependence on global commodity markets.

Across the border in Idaho, the somewhat ironically nicknamed “Gem State” moved on from mines long ago, stepping first into agriculture and forestry, and later into manufacturing, technology and services.

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As its economy developed, Idaho’s cities far outgrew their Wyoming counterparts. In 1890, Idaho’s population was 1.3 times larger than Wyoming’s. In 2017, it was three times larger. The Boise metro area alone is home to more people than in all of Wyoming.

And Boise is booming. Most newcomers have settled in the capital and the cities and suburbs surrounding it, compounding the state’s urbanization advantage. They appear to be drawn by the city’s combination of size and low cost of living.

Idaho has the fourth-cheapest cost of living in the country, according to a 2017 index from the Council for Community and Economic Research. Only Arkansas, Kentucky and Mississippi are cheaper. Wyoming is 29th.