About 18 million years ago a tectonic upheaval began that profoundly marked the present Lake Mead NRA landscape.
Thirteen million years ago, the crust around the Lake Mead area was stretched and thinned so iron and magnesium-rich magma and basalt, poured out of the ground and covered the landscape. The darker lava produced many of the black volcanic flow-capped mesas, such as Fortification Hill and Callville Mesa, seen in many parts of Lake Mead National Recreation Area.
Mineral-rich fluids trapped in older rock were mobilized when hot magma was injected into them. These hot, hydrothermal fluids percolated up through some of the igneous rock formations, including the Paint Pots pluton at the base of Fortification Hill, imparting their beautiful coloration!