Capitol Reef National Park - Geology

Geology

The area including the park was once the edge of an ancient shallow sea that invaded the land in the Permian, creating the Cutler Formation. Only the sandstone of the youngest member of the Cutler Formation, the White Rim, is exposed in the park. The deepening sea left Carbonate deposits, forming the limestone of the Kaibab Limestone, the same formation that rims the Grand Canyon to the southwest.

During the Triassic, streams deposited reddish-brown silt, which later became the siltstone of the Moenkopi Formation. Uplift and erosion followed. Conglomerate, itself followed by logs, sand, mud, and wind-transported volcanic ash, then formed the uranium-containing Chinle Formation.

The members of the Glen Canyon Group were all laid down in the middle to late Triassic during a time of increasing aridity. They include:

• Wingate Sandstone: Sand dunes on the shore of an ancient sea.
• Kayenta Formation: Thin-bedded layers of sand deposited by slow-moving streams in channels and across low plains.
• Navajo Sandstone: Huge fossilized sand dunes from a massive Sahara-like desert.

The San Rafael Group consists of four Jurassic period formations, from oldest to youngest:

• Carmel Formation: Gypsum, sand, and limey silt laid down in what may have been a graben that was periodically flooded by sea water.
• Entrada Sandstone: Sandstone from barrier islands/sand bars in a near-shore environment.
• Curtis Formation: Made from conglomerate, sandstone, and shale.
• Summerville Formation: Reddish-brown mud and white sand deposited in tidal flats.

Streams once again laid down mud and sand in their channels, on lakebeds, and in swampy plains, creating the Morrison Formation. Early in the Cretaceous, similar nonmarine sediments were laid down and became the Dakota Sandstone. Eventually, the Cretaceous Seaway covered the Dakota, depositing the Mancos Shale.

Only small remnants of the Mesaverde Group are found, capping a few mesas in the park's eastern section (see Geology of the Mesa Verde area).

Near the end of the Cretaceous period, a mountain-building event called the Laramide orogeny started to compact and uplift the region, forming the Rocky Mountains and creating monoclines such as the Waterpocket Fold in the park. Ten to fifteen million years ago, the entire region was uplifted much further by the creation of the Colorado Plateaus. Remarkably, this uplift was very even. Igneous activity in the form of volcanism and dike and sill intrusion also occurred during this time.

The drainage system in the area was rearranged and steepened, causing streams to downcut faster and sometimes change course. Wetter times during the ice ages of the Pleistocene increased the rate of erosion.