Mesa Verde | GeologyVirtualTrips

MESA VERDE NATIONAL PARK

FIELD TRIP STOP - MESA VERDE NATIONAL PARK, COLORADO

(Geology as it relates to Landscape and Human Culture)

LOCATION: Mesa Verde National Park is located about 50 miles west of Durango, Colorado along US-160. This park is situated in the Four Corners Region of the Colorado Plateau, a region of the Southwestern United States where Arizona, New Mexico, Colorado, and Utah meet.

GEOLOGIC FEATURES: Transgression; Regression; Coal Seams; Weathering, Erosion and Mass Wasting;

DESCRIPTION: Mesa Verde National Park was established to preserve the Cliff Dwellings of the Anasazi Indians (Ancestral Pueblo people). These structures, occupied approximately between 1200 and 1300 AD, were built beneath the overhangs of alcoves found high within cliffs of the Cliff House Sandstone. The alcoves were formed naturally through the physical and chemical weathering and mass wasting of porous sandstones (largely by frost-wedging) located above impermeable shale layers.. The spalling of sandstone slabs from the Cliff House Formation left broad spacious archways beneath overhangs that were then used as living space with buildings constructed of sandstone brick and mortar.

Listed stratigraphically (youngest rock on top), the Upper Cretaceous rock formations (about 75 to 86 mya) found within the Park are noted below along with their environments of deposition. The youngest three formations are commonly referred to as the Mesaverde Group. Ultimately, uplift initiated during the Tertiary Laramide Orogeny and subsequent erosion accounts for the present topography.

Cliff House Sandstone – Gray to Orange-Yellow/Buff sandstone representing marine, nearshore deposits. Commonly thick-bedded. The deeper waters of the Cliff House Sands indicate a transgressive period. Formational thicknesses vary around 400 ft.

Menefee Formation – Gray and Gray-Orange Cross bedded Sandstone with dark carbonaceous shales and coal representing coastal swamps and river floodplains indicating very shallow waters and further regression Thickness is between 350 to 400 ft.

Point Lookout Sandstone – The Upper part is resistant yellow-brown (tan) sandstone representing shallow water sands including beach and nearshore marine deposits. The lower part of the formation has interbedded brown sandstone and gray shale and is transitional with the Mancos lithology. A regression is indicated by the shallower deposits of the Point Lookout. Thicknesses vary between 330 to 375 ft.

Mancos Shale – Gray shales representing relatively deep, quiet-water deposits of mud. Thicknesses vary between 2000 and 2240 ft. The Mancos Shale represents a marine transgression over the shallower water deposits of the Dakota Sandstone.

STUDENT QUESTIONS:

(1) Define Transgression and Regression. How do they differ?

(2) Using the rock formations in the Park, briefly explain the evidence used to suggest periods of transgression and regression.

(3) Name two possible causes to explain a Transgression (or Regression).

(4) CHALLENGE: Name two or more possible ways that an environment can change in a given area over time.

(5) CHALLENGE: Besides sediment size, what characteristics of a sedimentary rock could indicate environment of deposition?

(6) CHALLENGE: Suggest reasons why the Anasazi people might have felt the need to build and occupy the Cliff Dwellings.

SELECTED REFERENCES:

-Harris, A. and E. Tuttle. 1983 (3rd ed.). Geology of the National Parks. Kendall/Hunt Publishing Company. Dubuque, IO. 554 pp.

-Harris, D.V. and E.P. Kiver. 1985 (4th ed.). The Geologic Story of the National Parks and Monuments, John Wiley and Sons, New York, 464 pp.

-National Park Service. The Geology of Mesa Verde. Accessed on 11/16/22: https://www.nps.gov/meve/learn/nature/geology.htm.

-Santucci, Vincent L. and Justin S. Tweet. Mesa Verde National Park Guide to the Fossils of the Cretaceous Cliff House Sandstone. National Park Service, U.S. Department of the Interior. Accessed on 11/16/22:

http://www.npshistory.com/publications/meve/cretaceous-cliff-house-fossils.pdf

-USGS. Geology of Mesa Verde National Park by Geology and Ecology of National Parks. Accessed on 1116/22:

https://www.usgs.gov/geology-and-ecology-of-national-parks/geology-mesa-verde-national-park

PHOTOS:

Figure 1 - Cliff Palace is the largest cliff-dwelling in North America. It was established in about 1200 AD by the Ancestral Pueblo people (Anasazi) and housed about 100 people. The dwelling area measures about 200 ft across and 80 ft high. Cliff Palace contains 150 rooms and 23 Kivas (large circular rooms that are sunken and used in ceremonies). Materials used in construction include sandstone blocks, mortar, and wooden beams. Note the crowd of tourists to the right of the photo.

Figure 2 - Note the dark streaks of Desert Varnish on the rock face. This coating is often found on exposed rock surfaces in arid region and results from the bacterial oxidation of manganese. This photo is taken from the platform pictured in Figure 3.

Figure 3 - Hikes down to the Cliff Palace are only led by Park Rangers and begin on this platform, the Cliff Palace Overlook.. The Cliff Palace is below and to the left of the platform. Walls of the Cliff House Sandstone separated by a shaly unit are seen in the upper right quarter of the photo.

Figure 4 - Spruce Tree House is the third largest village in the Park. It contains 130 rooms and 8 Kivas. The dwelling area measures about 216 ft across and 89 ft high, and served to house 60-80 people.

Figure 5 - Overall 600 cliff dwellings exist within the Park. 75% of the dwellings consist of 1-5 rooms each. Small structures can bee seen in the middle of the upper sandstone package.

Figure 6 - Close-up of Figure 5.

Figure 7 - The Cliff House Sandstone as exposed near the Geologic Overlook located at the north end of the Park. Note that is is more shaly with thinner sandstone beds than the same formation found near the major Cliff Dwellings found 7 miles to the south which are much more massive.

Figure 8 - The Menefee Formation stratigraphically lies directly below the Cliff House Sandstone. Its sandstone and carbonaceous shales and coals (dark layers) represent coastal swamps and floodplains. This photo was taken along the the Park Road just east of the Park Point Overlook. Irregularly shaped bedding surfaces likely indicate streams moving through the floodplain and swamps.

Figure 9 - Menefee Formation as exposed on the Park Highway near Park Point Overlook.

Point Lookout,Sandstone

Mancos Shale

Figure 10 - From Park Point Overlook. The gray Mancos Shale is seen below the resistant yellow-brown sandstone of the Point Lookout Sandstone.

Figure 11 - The 4 main rock formations in the Park are seen from Geologic Overlook and can be identified through the use of a sign provided by the National Park Service.

Menafee Fm,

Point Lookout,

Mancos Shale

Figure 12 - Photograph of the Mancos Shale, Point Lookout Sandstone, and Menefee Formation as depicted on the sign of Figure 11.