By Julie Etra

The Central Valleys (Spanish: Valles Centrales) of Oaxaca—also known as the Oaxaca Valley—are a geographic region encompassing the municipalities of Etla, Centro, Zaachila, Zimatlán, Ocotlán, Tlacolula, and Ejutla. This area is home to important and well-known archaeological and cultural sites, including Monte Albán, Tule, and Mitla, as well as lesser-visited sites such as Yagul and the Guilá Naquitz Cave.

The cave is especially notable as the verified birthplace of the oldest distinctly recognizable ancestor of modern annual corn: teosinte, a perennial grass with tiny mazorcas (corn ears) about the size of a slender finger. More on that in a bit.

Geography and Climate
The Y-shaped valley lies at the intersection of two major Oaxacan mountain ranges: the Sierra Madre del Sur and the Sierra Madre de Oaxaca (colloquially known as the Sierra Norte), which is an extension of the larger Sierra Madre Oriental. (Sierra means “mountain range.” For context, I live on the eastern side of the Sierra Nevada in northern Nevada—which, once upon a time, was part of Mexico.)

Oaxaca City sits at the heart of the valley at an average elevation of 1,550 meters (5,115 feet). With access to water from the Río Atoyac and Río Salado (though not in great shape today), the area has long been attractive for settlement. The valley spans more than 3,375 square kilometers (1,303 square miles), with about 1,100 km² (700 mi²) of arable land—by far the largest stretch of flat, farmable land in this mountainous state.

The Tlacolula Valley stretches 50 kilometers (31 miles) east, the Zimatlán Valley runs 100 kilometers (62 miles) south, and the Etla Valley extends 40 kilometers (25 miles) northwest.

The climate is subtropical highland, with warm temperatures year-round—something that often surprises winter visitors. Rainy and dry seasons are distinct, much like the coast, though less extreme. The valley averages about 69.5 cm (27.4 inches) of rainfall per year. Winter temperatures hover around 17°C (63°F) in November through January, rising to around 22°C (72°F) from May through August.

Geology
The Valley of Oaxaca has an ancient and complex geology. It features a mix of Precambrian metamorphic rocks (dating back 4.6 billion to 541 million years), Mesozoic sedimentary layers (252 to 66 million years ago), and Tertiary igneous rocks (66 million to 2.6 million years ago).

The valley floor is composed of gneisses (coarse to medium-grained metamorphic rocks) and mylonites (fine-grained rocks found along fault zones). Surface rocks include schists, granodiorite, and limestones, the latter indicating the presence of an inland lake or sea in the distant past. Sediment from surrounding mountain erosion has also filled much of the valley.

This is a tectonically active zone—part of the Oaxaca Fault System, where the Cocos Plate subducts beneath the North American Plate along the Middle American Trench. That’s why Oaxaca is so seismically active: about 25% of all earthquakes in Mexico occur here. The January 14, 1931, earthquake, which registered 8.0 on the Richter scale, flattened the city.
Further reading:
http://www.wiki.santafe.edu/images/4/45/Ch3-1.pdf

Economy
Besides tourism and crafts (alebrijes, ceramics, textiles), the valley continues to support extensive agriculture. Crops include corn, sorghum, beans, wheat, melon, watermelon, garbanzo beans, and of course, agave (maguey) for mezcal production. Corn remains the most culturally and economically significant crop.

Today, you’ll also see large greenhouses growing ornamental plants—visible when flying in with Aerotucán or driving into the valley from the south via Highway 175. Flowers such as flor de cempasúchil (marigolds, genus Tagetes), flor de borla or cresta de gallo (Celosia argentea, aka cockscombs), and terciopelo (velvet flower) are cultivated for Day of the Dead altars (ofrendas). Roses are also grown here and sold in markets, including those in La Crucecita.

Important
Archaeological Sites

Yagul
Located midway between Oaxaca City and Mitla on Highway 190, Yagul is a former Zapotec city-state first settled around 500–100 BCE. It remained occupied up through the Spanish conquest. The name “Yagul” is Zapotec: ya means tree and gul means old—“old tree.” (What specific tree? That remains a mystery.)

Excavated in the 1950s and 60s by archaeologists Ignacio Bernal and John Paddock, Yagul is built around a hill and includes a large ball court, palaces, temples, and tombs. Building materials included cobbles from the Río Salado and volcanic rock like basalt. The community likely reached its peak between 1250 and 1521 CE. After the conquest, much of the population relocated to nearby Tlacolula, which now hosts a well-known and colorful market.

Guilá Naquitz Cave
This site is particularly close to my heart. Back in the 1980s, as a student at Colorado State University, we had a few teosinte plants on the university farm. As a grad student, one of my jobs was to help propagate heirloom corn (maíz criollo) seeds to preserve their genetic integrity. Years later, DNA mapping confirmed that teosinte was indeed the ancestor of modern corn—and that it originated here, in Oaxaca.

Guilá Naquitz Cave (Zapotec for “white cave”) is located about 5 km (3.1 mi) northwest of Mitla, likely in a limestone outcrop. This site is of enormous ethnobotanical and paleobotanical importance, documenting the early domestication of crops like teosinte, squash (Cucurbita spp.), bottle gourds (Lagenaria siceraria), and beans.

Inhabited as early as 10,000 years ago, the area once supported a rich variety of edible plants consumed by hunter-gatherers—acorns, wild fruits and berries, prickly pear cactus (tuna), agave, nuts such as yak susí (the identity of which remains unclear), wild onions, and more. Sadly, centuries of land-use change have greatly diminished this ecosystem. The cave is located at the base of a cliff at an elevation of 1,926 meters (6,319 feet).

Highlighted Communities in the Valley
Here’s a small, somewhat random selection of communities we’ve passed through on our drives to Oaxaca City:

Ejutla de Crespo
Located at the southern end of the valley, Ejutla means “place of abundant greens” in Nahuatl. “Crespo” refers to Manuel Sabino Crespo, a contemporary of Morelos during the War of Independence. The town’s economy centers on agriculture and mezcal production.

Ocotlán de Morelos
With a population of around 23,000, this town was bypassed about a decade ago when a new commercial route diverted traffic away from its bustling central square. The name Ocotlán comes from Nahuatl and means “among the ocote trees,” referring to the pine species found descending from the oak-pine woodlands above. The suffix honors José María Morelos y Pavón, Catholic priest and independence leader. Agriculture is the main economic driver.

San Bartolo Coyotepec
Just five kilometers (three miles) south of Oaxaca City, this town is famed for its barro negro (black clay) pottery. The shiny finish comes from polishing and specific firing techniques. There’s a wonderful little museum on the west side of the main highway. Years ago, my sister and I eavesdropped on a workshop there.

Villa de Zaachila
This town and municipality is 6 km (3.7 mi) south of Oaxaca City along Highway 131. Before the conquest, it was the main city-state after the fall of Monte Albán. The name may refer to its 14th–15th century ruler Zaachila Yoo—or it may mean “large leaf of the purslane” (Portulaca oleracea), a crunchy succulent considered a weed in the U.S. but a valued quelite in Mexico. You’ll often find verdolaga in local markets and dishes (see The Eye Archives:
http://www.theeyehuatulco.com/?s=quelites).