Geoscience Reference
In-Depth Information
In the time prior to the cliff-dwelling period, ancestral
Pueblo people tended to live in small villages that were
scattered around the upland areas. By about 1000 years
ago, people had begun concentrating in larger villages along
the canyon rims. Archaeologists believe that the move down
into the canyons by the ancestral Pueblo around
a
.
d
. 1100
and the associated construction of elaborate cliff dwellings
reflect the increased concentration of people into villages
that were highly defensible. The buildings were constructed
of bricks made of hard sandstone that were held together
with a mortar mixed of mud, sand, and water called
adobe
.
Fantastic cliff dwellings can be seen in a variety of places
in the southwestern United States, such as Canyon de Chelly
in Arizona, Bandalier National Monument in New Mexico, and
Mesa Verde in Colorado. Although these sites are 700 to 800
years old, they clearly were built by people living in a complex
culture, with villages occupied by hundreds to thousands of
people. The structures ranged in size from one-room storage
units to large, multipurposed buildings with more than 150
rooms. Ceremonial rooms (called
kivas
), which were used for
religious ceremonies, are present at many sites, as are open
plazas where cultural and civic events took place.
Utah
Colorado
Mesa Verde
National Park
Canyon de Chelly
National Monument
Bandalier National
Monument
Arizona
New Mexico
(c)
Location of famous sites in the southwestern United States
where cliff dwellings are found.
If you visit such places, think about geologic time and
how it relates to these amazing archaeological ruins. For
the sandstone and shale to be present, sediments must
have accumulated in a sea or ocean that varied in depth
over a long period of time. This sea then disappeared, and
sediments slowly lithified to become rock. Somewhere
along the line, over millions of years, streams slowly cut
into the rock to form the canyons in the area. At the same
time, the niches gradually formed due to salt-crystal
growth. Very late in this sequence prehistoric people
moved into the area and built these structures. Although
no one has lived in them for at least 700 years, the niches
remain essentially unchanged. We know this because
the ruins that lie within the niches are in phenomenal
condition.
What prompted the ancestral Pueblo to leave their
elaborate cliff dwellings? No one knows for sure. The
best scientific guess is that the Pueblo were influenced
by a variety of factors, including climate change, drought,
deforestation, and competition from other cultural groups.
Regardless, their descendants live on in the modern Tanoan
and Hopi peoples who live in the region today.
(b)
This structure is a room for religious ceremonies called a
kiva
.
People entered the room by way of the ladder poking through the
opening at the top of the structure.
Hydrolysis
Hydrolysis
is a weathering process that decom-
poses silicate minerals within rocks. This form of weathering
occurs when silicate molecules are split after the addition of
hydrogen and hydroxyl ions derived from water. In granitic
Hydrolysis
A chemical weathering process that results in the
decomposition of silicate molecules within rock through the
reaction of hydrogen and hydroxyl ions in water.
