We're looking for a central Mexican state for today's Geo Quiz.

It lies northwest of Mexico City.

The answer is the state of Queretaro.

Queretaro is home to the Sierra Gorda Biosphere.

It's a protected wilderness area roughly the size of Rhode Island.

Conservationists hope the reserve will attract eco-tourists....

giving the local economy a much-needed boost.

There are mountains and rivers to explore ...and something called the Sotano del Barro.

Sotano del Barro

It's a massive hole in the side of a mountain....a deep underground well created millions of years ago by shifting tectonic plates.

Our reporter Jason Margolis went hiking to see the Sotano at sunrise.

Sotano at sunrise

So before the crack of dawn, he was on the trail: Listen