Moenkopi Formation

Moenkopi Formation paleoenvironment 240 Ma
Depiction of the Colorado Plateau region during the deposition of the Moenkopi Formation, ~240 million years ago. Location of Zion National Park is indicated.

Paleogeographic map courtesy of Ron Blakey, Colorado Plateau Geosystems, Inc.

Moenkopi outcrop near Rockville, Utah
Thin layers of mudstone, siltstone, and sandstone of the Moenkopi Formation

NPS photo/Adrienne Fitzgerald

Early-Middle Triassic
~240-250 million years ago

The Moenkopi Formation consists of thin layers of reddish-brown mudstone, sandstone, and siltstone that were deposited on broad tidal flats, in slow-moving rivers, and floodplains of a broad coastal plain. Limestone layers also occur within the Moenkopi, evidence of slightly higher sea levels and encroaching shorelines. Seawater evaporating on this broad, arid tidal flat left behind thin layers of gypsum throughout the Moenkopi.

Moenkopi with ripple marks

NPS photo

Many sandstone and mudstone layers of the Moenkopi contain ripple marks, evidence of water and waves moving these sediments. Footprints of early reptiles and possibly amphibians have been preserved in Moenkopi mudstones across Utah, recording their movements as they wandered across the slick prehistoric mudflats that once covered the region.

Moenkopi outcrop near Virgin, Utah
Moenkopi Formation as seen along State Route 9 near Virgin, Utah. Cliff band at top of mesa is the Shinarump Member of the Chinle Formation.

NPS photo/Adrienne Fitzgerald

The Moenkopi Formation outcrops in two parts of Zion National Park: near the entrance to the Kolob Canyon Scenic Drive, and in the southwestern part of the park near Rockville and west of the Chinle Trail. Large exposures of the Moenkopi, over 1,000 feet thick, can be seen along State Route 9 when approaching the park from the south.

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Last updated: June 13, 2015

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