100 years ago last week, the Grand Canyon was established as the 17th National Park. Covering nearly 2,000 square miles of incredible desert wilderness, the Grand Canyon is consistently among the most visited parks and is recognized globally as a true wonder of the world.

While the canyon layers were formed long before dinosaurs roamed, fossils of ancient marine animals are often uncovered – some dating back 1.2 billion years.

The Great Unconformity refers to a gap in the rock record between Cambrian times (~550 m.y. ago) and the pre-Cambrian (anything earlier). An unconformity is a surface in the rock record, in the stratigraphic column, representing a time from which no rocks are preserved — a geological mystery of epic proportions.

Meaning 250 million-year-old sediment layers can be found right on top of layers holding those very same billion-year-old fossils. What happened to the millions of years in between? Nobody knows yet.

Of the many unconformities observed in geological strata, the term Great Unconformity is frequently applied to either the unconformity observed by James Hutton in 1787 at Siccar Point in Scotland or that observed by John Wesley Powell in the Grand Canyon in 1869.

These are both exceptional examples of instances where the contacts between sedimentary strata and either sedimentary or crystalline strata of greatly different ages, origins, and structure represent periods of geologic time sufficiently long to raise great mountains and then erode them away.

Carved over hundreds of millions of years by the Colorado River and measuring 277 miles (446 km) long, up to 18 miles (29 km) wide, the Grand Canyon is a major natural phenomenon, but it is also a place of deep historical mysteries and oddities as well.

It's days like today when I feel the most grateful to live where I do and to be able to appreciate so much of the great outdoors. To be able to climb and hike rocks that have existed for hundreds of millions of years.