Joints in Jurassic Entrada Sandstone
Fiery Furnace, Arches National Park, Utah

The Entrada Sandstone was deposited in coastal dunes during the middle Jurassic. Most of the arches in this national park are developed in this resistant sandstone. During the late Cretaceous and early Tertiary, the sedimentary rocks were folded into a gentle anticline and fractured into joints. The joints were enlarged and eroded during the colder and wetter episodes of the Pleistocene.

The Fiery Furnace is named for their red glow at sunset. The jointed sandstone fins hide at least 18 arches and 1 natural bridge. Because of the tricky route finding, access to this area is restricted to ranger-led hikes.

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