Volcanic Boulders When Boulder Mountain, west of Capitol Reef National Park, exploded two million years ago it sent giant boulders flying. Millions of years of enormous debris flows and floods rounded the boulders and dumped them across broad valley floors beyond the mountains. Rivers have since cut deeply into those valley floors, carving canyons. The old valley floors are now mesas that rise up to 600 feet above present river valleys. The boulders you see in this photo are almost 100 miles from Boulder Mountain near what is now Highway 70 on the San Rafael Swell in South Central Utah. Boulders like these can be found in many parts of Arches, Capitol Reef, National Parks and and Grand Staircase Escalante National Monument. The stark, rich black rocks give strong contrast to the bright red sand that covers the area. Beautiful combinations of light, texture, and color are abundant. See more of the Utah National Parks and Monuments at Outdoor Scenics: Photography by Allen Adler - Capturing the beauty and color of Nature.