Today, as the venerable Chaco Culture National Historical Park celebrates the 28th anniversary of its NHP redesignation, scientists continue to explore a sophisticated artifact of pueblo culture and speculate about its functions. While most foot trails produced by aboriginal cultures disappeared centuries ago, the Chaco Culture produced an extensive, carefully engineered road system still evident in the landscape of the Colorado Plateau.

Chaco Culture NHP is a low-profile national park (2007 visitation 68,211), but it has much to offer visitors and even more to hold the attention of archeologists and other scientists. When we invest the extra effort it takes to get to this remote park in the San Juan Basin of northwestern New Mexico, we’re rewarded quite handsomely. Here’s a place with some of the most impressive ruins in the entire Southwest. (Just seeing the Pueblo Bonito great house makes the trip worthwhile.) Small wonder that it was designated a World Heritage Site in 1987.

Chaco Canyon was the administrative, economic, and ceremonial hub of a thriving Ancestral Puebloan culture that dominated the Four Corners area of the Colorado Plateau between about AD 850 and 1250. Given that this society flourished ten centuries ago and more, we can’t help but be impressed by Chaco’s high level of social organization, more than a dozen massive stone structures (“great houses”), large scale public architecture, complex ceremonial life, and far-flung trade links. Indeed, where architectural accomplishment and social organization are concerned, the Chaco Canyon complex is considerably better developed than its much more highly publicized counterpart at Mesa Verde.

Scientists find the Chaco region and its artifacts endlessly fascinating. Despite numerous studies over the past century, there are still many features of this remarkable cultural complex that remain to be figured out. Some of the most interesting question marks involve basic concepts of location, design, and construction. For example, investigators still aren’t quite sure why was this particular site, which has many locational drawbacks, was selected to serve for centuries as the major hub of the Chaco Culture. They continue to speculate why this cultural landscape, the product of many generations of toil and sacrifice, was abandoned by the mid 1200s. And they would very much like to get a better understanding of why the Chacoans constructed a road system that was remarkably sophisticated for its time, and which has some very quirky design features.

Ground surveys, aerial photography, and more sophisticated remote sensing technology have revealed that the Chacoans built more than 400 miles of 20- to 40-foot wide roads, including some major ones radiating outward from Chaco and numerous shorter segments emanating from dozens of scattered settlements. For a partial map of the network, including hypothesized as well as known segments, see this site.

Most of the roads were constructed for reasons that are easy to grasp. Like modern roads, they served as links to resource areas and other communities, providing convenient routes for communication and trade. But some of the roads the Chacoans built seem to lack clear destinations, and this raises the question of whether a utilitarian purpose prompted their construction. An even more fundamental question is why a society that lacked wheeled vehicles and draft animals went to the great trouble of building carefully engineered roads instead of just relying on trails and traces. And why did they have an obsessive concern for linearity, sometimes investing great effort in building stairways and other passages over terrain obstacles that could have been easily bypassed? As the answers to these and related questions about the roads are worked out, we’ll be able to describe the Chaco Culture in less speculative terms.

The layout of the roads shows considerable concern for cardinal, solar, and lunar directions. (This is dramatically evident in the lengthy North Road and its South Road counterpart.) Further, recent scientific studies have shown that most of the roads were short (only a few kilometers), many did not connect the originating community with any other, and roads generally did not help to minimize travel distance between settlements. These characteristics have convinced most scientists that the Chacoan road network, like the public architecture and ceremonial sites of the urban center in Chaco Canyon, reflects a grand design rooted in the Ancestral Puebloan world view. This means that religious beliefs and local politics probably trumped economic concerns like the need to link settlements, access resources, and facilitate trade. And since this prehistoric road system did not serve integrative economic and political interests, it did not define the spatial extent of Chacoan influence.

The road pattern nevertheless appears to reinforce Chaco Canyon’s stature as the “center place,” at least in a regional context. Like the postal road system that evolved in historic France, where all roads led to Paris, the salient routes in the Chacoan road system converged in the Chaco vicinity and the roughly 150 outlying settlements were not road-linked to each other.

By the mid 1200s Chaco had lost its status as a regional central place. The Ancestral Puebloans migrated elsewhere, and the road system, abandoned great houses, and other cultural features and forms began deteriorating and returning to nature. The ruins at Chaco Canyon eventually attracted the attention of white settlers and scientists, leading to the establishment of Chaco Canyon National Monument on March 11, 1907. On December 19, 1980, the Monument was redesignated Chaco Culture National Historical Park and 13,000 acres were added to the park.