Portfolio Milestone

Portfolio Milestone

GEO101 Earth Sciences

Colorado State University Global

Earth Science in a National Park – Arches National Park

Section 1 – Introduction

Thesis – The natural formations found at Arches National Park are truly an unbelievable wonder to behold, but the story of their formation is far from unimaginable.

Section 2 – Geologic Story

Important Time Periods

300 Ma – Pennsylvanian Period

200 Ma to 140 Ma – Jurassic Period

65 Ma – Tertiary Period


Navajo Sandstone

Entrada Sandstone

More than 300 million years ago, an inland sea that filled the Paradox Basin of the Colorado Plateau evaporated leaving a salt bed, thousands of feet thick in some areas, exposed. This salt bed was eventually covered by debris during the Uncompahgre Uplift. Some 200 million years ago, during the Jurassic Period, the Navajo Sandstone that is prevalent in this region was deposited. Over the next 70 million years, sediment brought in by the wind and rain covered the land in another 5,000 feet of Entrada Sandstone (Kiver & Harris, 1999). Today, most of those deposits have eroded away leaving us with the formations we see currently.

Section 3 – Plate Tectonics

Salt Tectonics

Park does not lie on a plate boundary


Moab Fault Line

Arches National Park isn’t near a plate boundary and is actually heavily influenced by “salt tectonic” (Castleton, Erickson, and Kleber, 2018). Salt is relatively weak in the world of geology, and when heavy loads are applied to it the salt beds become very unstable (Hudec & Jackson, 2007). The Moab Fault is a 28 mile long “normal fault” bordered by a damage zone made of many minor structures such as “branch points, fault bends, overlap zones, and fault related folds” (Foxford, Garden, Guscott, Burley, Lewis, Walsh & Watterson, 1996). This fault was fairly active from the Triassic to mid-Cretaceous periods (Foxford, et al., 1996).

Section 4 – The Geography

Physical Features

2,000+ arches


Ephemeral Pools

Black Ground Cover

The park is obviously most noted for its arch formations of which there are more than 2,000. In addition to these formations are the fins. Fins are narrow walls of hard sedimentary rock that remain after heavy erosion (Scorsone & Zitzmann, 2014). Ephemeral pools are more commonly known as “potholes” that occur naturally in sandstone basins (Whitford & Duval, 2020). The biological soil crust found in this region appears as a thick crusty looking ground covering. It consists of “cyanobacteria, lichen, mosses, green algae, and microfungi” and is found throughout southern Utah (National Park Service, 2020). The fibrous ground cover keeps soil particles together which creates a layer that resists erosion better.

Section 5 – Weather and Climate


High desert region with high fluctuations in temperature


Köppen Climate Classification

As a part of the Colorado Plateau, Arches National Park is a high desert that can experience a wide range of temperatures from day to day and month to month. In the peak of the spring and summer months, temperatures can range from 60 to 100 degrees Fahrenheit with night time lows dropping to 30 degrees. The climate of the region falls into the BSk subgroup of the Köppen Climate Classification scale (Weather Atlas, 2020). This means that the park experiences tropical and subtropical climate types with hot summers and cold winters.

Section 6 – Conclusion

Formation to millions of years

Water and wind erosion

Composition of the land

Arches National Park is a magical and absolutely striking region of the Colorado Plateau who’s story began hundreds of millions of years ago. Although the land seems impossible with its sprawling fins, deep red plateaus and fiery orange arches and windows, the creation of these marvels is completely natural and easily explained.


Castleton, J. J., Erickson, B. A., & Kleber, E. J. (2018). Geologic Hazard of the Moab Quadrangle, Grand County, Utah. Special Study 162 Utah Geological Survey. doi:978-1-55791-945-8

Foxford, K. A., Garden, I. R., Guscott, S. C., Burley, S. D., Lewis, J. J., Walsh, J. J., & Watterson, J. (1996). The Field Geology of the Moab Fault. Utah Geological Association, 265-284. doi:http://archives.datapages.com/data/uga/data/067/067001/265_ugs670265.htm

Hudec, M. R., & Jackson, M. P. (2007). Terra infirma: Understanding salt tectonics. Earth-Science Reviews, 82(1-2), 1-28. doi:10.1016/j.earscirev.2007.01.001

Kiver, E. P., & Harris, D. V. (1999). Geology of U.S. parklands (5th ed.). New York, NY: John Wiley.

National Park Service. (2020, February 15). Biological Soil Crust of Southeast Utah (U.S. National Park Service). Retrieved June 08, 2020, from https://www.nps.gov/articles/seug-soil-crust.htm

Scorsone, A., & Zitzmann, M. (2014, August 05). Geology of Arches National Park. Retrieved June 08, 2020, from https://web.uri.edu/geofieldtrip/geology-of-arches-national-park/

Weather Atlas. (2020). Arches National Park, UT – Detailed climate information and monthly weather forecast. Retrieved June 08, 2020, from https://www.weather-us.com/en/utah-usa/arches-national-park-climate

Whitford, W. G., & Duval, B. D. (2020). Ecology of desert systems (2nd ed.). London, United Kingdom: Academic Press. doi:https://doi.org/10.1016/B978-0-12-815055-9.00004-7