October 07, 2015
Geology and time have been majestically creative in Capitol Reef National Park’s remote Cathedral Valley. The picturesque red-rock valley, accessible via a rough outback road in south-central Utah, boasts not only a pair of towering "cathedrals,” or monoliths, known as the Temple of the Sun and the Temple of the Moon, but also a mountain of glass. (Well, sort of.)
In this photograph, taken on Sept. 12, 2015, the paired, pyramid-like “temples” rise beyond the gleaming flanks of a hillock dubbed Glass Mountain, even though it's only about 15 ft (4.5 m) high. The mound is impressive, though: It's packed with big gypsum, or selenite, crystals that gleam and glitter in sunlight. The Utah Geological Survey says the gypsum coalesced in evaporating seawater about 165 million years ago. Initially buried in sediment, the gypsum gradually percolated upward via faults and accumulated in domes like Glass Mountain.
The nearby Temple of the Sun and Temple of the Moon are remnant outliers of Entrada sandstone and siltstone that formed in vast sandy/muddy tidal flats about 160 million years ago, during the Middle Jurassic, the Geologic Survey explains. The area’s overlying Curtis Formation, still visible capping a plateau rimmed with possible future monoliths, eroded away over the eons, stranding the Temples within Cathedral Valley.