Question:Why is Arizona's "Red Rock Country" red?Answer: Arizona's Red Rock Country, which includes Sedona, Oak Creek Canyon and surrounding areas, is world famous for its spectacular ruddy views. Last year, "USA Today Weekend" magazine declared it the most beautiful place in the nation.
How did the Red Rock Country come by its ocher tint?
Larry D. Fellows, director of the Arizona Geological Survey and a state geologist, explained where the redness comes from in the fall issue of the survey's newsletter, "Arizona Geology."
The red rock, Fellows says, was once mud and sand that piled up during a 50 million year stretch beginning 320 million years ago, when today's Sedona area was a dry coastal plain beside a shallow sea. Wind, rivers, ocean currents and waves laid down sediments as the sea level fluctuated over the millennia. During the times of high sea level, mud stacked on top of river sediments. When the sea level dropped, sand dunes covered the area. Eventually, the sediment compacted and turned to stone. All of this happened long before the dinosaurs stalked the land.
The wonderful red color, Fellows says, is the result of a thin layer of iron oxide (effectively, rust) that formed on the grains of the rocks due to chemical weathering when the rocks were exposed during the arid periods.
The red sediment sandwich in the Sedona area was once about 1,900 feet thick, Fellows says, but Oak Creek and its tributaries have gnawed away huge amounts of it. The erosion that exposed the stone lets us enjoy its beauty.
By the way, another rusty, rocky place that owes its red color to iron compounds is now being explored by NASA robots: Mars, the Red Planet.