At Echo Point west of Sydney, Australia, visitors have a panoramic view of The Three Sisters — spectacular remains of a huge sandstone outcrop, broken and teetering on the edge of a wide valley. In the distance you can see the same sedimentary strata in vertical cliffs that stretch as far as the eye can see. These sedimentary layers also travel out of sight under the earth—much further than many suspect, 100 km (60 miles) east to the Pacific Ocean, 200 km north and 200 km south. They form part of the Sydney basin, a geological structure where layers of sediments accumulated to a depth of 3 km.
You can see the same geological pattern when you stand on the rim of Grand Canyon in western USA. As you peer across the abyss you marvel at the horizontal rock layers that decorate the walls—the same pattern on both sides of the canyon. Some layers form sheer cliffs; others crumble into sloped aprons. With so little vegetation in the area, the layers stand out and can be traced into the distant haze. In fact, these sedimentary formations have been recognized over thousands of kilometres across North America.