The United States is the world's most powerful economy, but much of that power is derived from rather old-fashioned sources.

More than half of the country's electricity is produced by burning coal, and as demand for energy increases, so does the pressure on those who supply it.

Mention to the average American that you're going to Wyoming, and they are as likely as anything to ask you why. It is a fair question. Wyoming consists mostly of scrubby grassland or arid, tan-coloured mountains, and with just 500,000 people, it is the least populous state in the US.

But the people of America should be thankful to Wyoming, because its colossal treasure trove of natural resources is helping - literally - to power the US economy.