U.S. Bureau of Economic Analysis numbers show that 10 of Colorado's 64 counties accounted for 85 percent of the state's economic activity in 2015.
The Denver Post reports the 10 connecting counties stretch along the Front Range from Larimer and Weld in the north through Denver and down to El Paso in the south.
Denver, which accounted for an eighth of the population, made up about a fourth of the state's Gross Domestic Product at $76.6 billion.
Arapahoe County accounted for 13.6 percent of the state GDP at $41.7 billion. El Paso County, home of Colorado Springs, was the third highest at $28.9 billion, or 9.4 percent.
Stephan Weiler, an economics professor at Colorado State University, says about 95 percent of the state's growth between 2012 and 2015 occurred in the 10 counties.