The Rio Grande Gorge and the
Geology that Formed It
By Linda Thompson

Rio Grande
Gorge ©Terry
Thompson, HighMesaProductions.com
(Taos, New
Mexico) Spanish conquistadores discovered
the mouth of the Rio Grande River in 1519. In
the next 100 years they founded some of the
earliest North American settlements along its
banks. These explorers named the river El Río
Grande, or 'the Great River.' However, it has
been called many other names. The pueblo people
called it Posoge, or P'Osoge, 'big river.'
Shipwrecked British sailors crossed it in 1568
and called it 'the River of May.' Various
Spaniards and Mexicans named it El Río de
Nuestra Señora ('river of our lady'), El Río
Guadalquivir, El Río Bravo, El Río del Norte,
and El Río Turbio ('turbulent river'). On a map
dated 1700, it appears as El Río del Norte y de
Nuevo México.
This river of
many names, or at least the section that runs
through northern New Mexico, is not a typical
river that has carved out its own valley.
Rather, the valley appeared first and the river
followed. This 'rift valley' is a separation in
the earth's crust caused by faulting and other
earth movements when the North American and
Pacific plates scraped against each other some
twenty-nine million years ago.
The Rio Grande
Rift is not just the canyon, or gorge, that
holds the river, but an area of more than
160,000 square miles reaching from central
Colorado almost to Big Bend National Park in
Texas. Taos Plateau is part of this 'rift
system' and lies in the San Luis Basin, which is
nearly a hundred miles long and about
forty-seven miles wide. The San Luis Basin is
one of four major basins created by the faulting
and volcanic energy. Some scientists believe
that several million years from now the Rio
Grande Rift may become an ocean. If that should
happen, Taos County residents will have both
mountain and ocean views!
As pressures
from the scraping plates caused the earth's
crust to crinkle, Colorado and New Mexico rose
nearly 5,000 feet. Basaltic magma surged upward
from the mantle, forcing weaker areas of the
surface to spread. All of this faulting and
mountain-building activity was accompanied by
volcanic eruptions and lava flows. One eruption
formed Capulin Mountain National Monument, a
cinder cone east of Taos. Fault-enclosed basins
called grabens dropped several thousand feet
lower than adjacent land. Blocks of the earth's
crust fell into some of these grabens, deepening
them. Sediments including sand, gravel,
volcanic lava, and ash filled the grabens to
depths of four and a half miles in some places.
Meanwhile, the
Sangre de Cristo Range rose to the east and the
San Juans to the northwest. The Rio Grande,
then a stream trickling down from near
present-day Leadville, Colorado, flowed into
four basins forming a 340-mile-long line between
the river's headwaters and the vicinity of
Socorro, New Mexico. Today, the four basins-the
Upper Arkansas, San Luis, Española, and
Albuquerque Basins-range in length from about 50
to 150 miles, with an average width of 30
miles.
Several of New
Mexico's early pueblos are believed to have
experienced earthquakes as the rift continued to
develop. Some of the earliest people, the
Clovis and the Folsom, may have witnessed
volcanic eruptions some ten to twelve thousand
years ago. Occasional mild earthquakes continue
today along this rift.
The heat from
ongoing geologic activity shows up in hot
springs along the Rio Grande, including Ojo
Caliente, or 'Hot Eye,' southwest of Taos.
Native Americans enjoyed soaking in these
springs, just as do New Mexicans and tourists
today. In the nineteenth and twentieth
centuries, prospectors and miners flocked to New
Mexico attracted by deposits of gold, silver,
lead, copper, zinc, and molybdenum that rose
from deep in the earth as super-hot,
mineral-rich solutions along the Rio Grande
Rift.
The Rio Grande
is among the longest twenty-five rivers in the
world and the fourth or fifth longest in North
America. It starts near the Continental Divide
in the San Juan Mountains, runs 470 miles
through New Mexico to the border of Texas and
the Mexican province of Chihuahua, and empties
into the Gulf of Mexico. For about 1,250 miles
it forms the international boundary between the
two countries. The river is between 1,800 and
1,900 miles long overall, depending on how its
course changes from year to year.
Some of the
best places to view the Rio Grande Rift are:
(1) The
Overlook on N.M. Highway 68, about eight miles
south of the Ranchos de Taos post office. The
view from the pullout is spectacular. From
picnic areas on the east side of the road at
this point and 1.3 miles further south, you can
see the gash in the earth that is the river
gorge. The rift narrows and widens within a
short distance, creating 'buckets' that change
color as the sun moves across the sky. You can
also see distant mountains in Colorado to the
north, the snow-topped Sangre de Cristo Range on
the east, and the vast and serene Taos Plateau
spread out before you.
(2) The Rio
Grande Gorge Bridge. This bridge carries U.S.
Highway 64 across the river about thirteen miles
northwest of Taos. Sidewalks with observation
platforms at mid-span allow visitors to gaze
down at the narrow ribbon, 650 feet below. A
large picnic area on the southwest side of the
highway leads to a hiking trail along the
river's west rim.
(3) The Wild
Rivers Recreation Area about thirty-five miles
north of Taos. Head north on Highway 522 and
take Highway 378 about three miles north of
Questa. Here, the Red River flows into the Rio
Grande at La Junta Point. There are developed
campgrounds and a number of hiking trails,
including some that descend hundreds of feet to
the Rio Grande. Call the U.S. Bureau of Land
Management's Taos Field Office, (505) 758-8851,
for further information.
Recommended
book: Roadside Geology of New Mexico (Roadside
Geology Series) by Halka Chronic, Mountain Press
Publishing Company, 1987.
Helpful web
sites:
http://www.nm.blm.gov/recreation/taos/taos_rec_home.htm
http://geoinfo.nmt.edu/research/taos/home.html
http://home.att.net/~sgeoveatch/rio_grande_rift.htm
Information and photo submitted
by:
Article:
Linda Thompson
Photo: Terry Thompson
High Mesa Productions HCR 74 Box 22273 El Prado, New Mexico 87529
505-751-0051 |

Linda and Terry Thompson |
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Linda
Thompson, co-owner of High Mesa
Productions, writes children’s books
and magazine articles, among other
things. She is an online instructor
for U.C. Berkeley Extension’s
intermediate copyediting courses.
With her husband, Terry, she lives
in Taos, New Mexico, which they
consider to be like no other place
they’ve ever been. During their
joint and separate lives, they’ve
lived in the San Francisco Bay area,
Los Angeles, Seattle, rural England,
Barcelona, Honolulu, and Washington,
D.C. Now, their camera and keyboard
are mainly focused on the western
states and Texas, with occasional
excursions to other parts of the
world. See their
website for additional
background and experience. |
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