Few people forget their first visit to the Grand Canyon. The chasm does not reveal itself until you are nearly at its edge. And then it appears, over a mile deep, with a barely visible Colorado River winding through its heart.

Geologist and writer James Powell was as awestruck as anyone on his first-time visit. But wonder leads scientists to ask questions, and Powell wanted to know how and when the canyon formed. He tells the story in his new book, Grand Canyon: Solving Earth’s Grandest Puzzle.

The history of scientific discovery is necessarily the history of scientists, and Powell reverently describes the geologists who devoted their careers to the Grand Canyon. Major John Wesley Powell (no relation) was among the first to study it. On an 1869 expedition, he realized that the dramatic landscapes of the West could only be the work of rivers. At the time, the idea was controversial, but Powell’s disciples, Grove Gilbert and Clarence Dutton, went on to expand it, suggesting a role for continental uplift in the Grand Canyon’s formation.

The most significant breakthrough in the understanding of geological processes came in the 20th century: the realization that the Earth’s crust is composed of dynamic pieces that move over time. Powell writes, "The ultimate cause of the Grand Canyon is plate tectonics," which shifted the course of the Colorado River eons ago, so that it swallowed up lesser rivers and in the process carved the canyon.

Grand Canyon will appeal to those who have stared at the great chasm in amazement, and simply asked how it came to be.