Fire and Water: The Making of the Grand Canyon

摘要

John Wesley Powell first viewed the remnants of basalt lava adhering to the walls of the inner gorge in the western Grand Canyon more than a hundred years ago. Yet today this awesome record of relatively recent volcanic activity-recent being 250,000 to more than one million years ago-remains largely unknown. Each year, nearly five million tourists, approaching the canyon's northern and southern rims near the visitor centers, marvel at the two-billion-year geological record in the exposed rock and at the river's ability to erode a canyon one mile deep.