An aerial photo shows ancient linear roads that led to Pueblo Alto in Chaco Culture National Historical Park.

ADRIEL HEISEY

Drilling boom threatens web of ancient roads in Southwest

About 1000 years ago, indigenous people built an elaborate network of great houses, kivas, and grand roads centered on Chaco Canyon, in the middle of the San Juan Basin of present-day New Mexico. Today, the region is one of the nation's most productive oil and gas basins. It is also the setting of a collision between burgeoning energy development and archaeology, as new discoveries reveal the importance of the larger landscape in understanding Chacoan society.

Taking advantage of advances in drilling technology, more than 4000 new wells will be developed in the area in the coming years, predicts the Bureau of Land Management (BLM), which manages development of federal mineral resources. Late last month, a federal judge issued a decision that may encourage the sale of oil and gas leases and eventual drilling near the Chaco Culture National Historical Park and known ancient roads. As a coalition of environmental and tribal groups mulls an appeal, they also await a new management plan from BLM, due as early as next month. With President Donald Trump's administration pushing for more oil and gas development on public lands, they worry the new plan may favor development at the expense of cultural and environmental protection.

Meanwhile, advances in remote sensing are revealing hundreds of previously unknown roads between Puebloan sites. As companies scrape well pads and access roads from the high desert scrub, archaeologists fear they will erase ancient roads before they have been fully studied—or even detected. "This real intense development that they're talking about essentially transforms the landscape into an industrial park," said John Roney, an independent cultural consultant based in Albuquerque, New Mexico, who formerly worked for BLM and conducted the first aerial survey of Chaco roads.

Although the park encompasses the largest pueblo, hundreds of smaller sites dot a 100,000-square-kilometer area surrounding the point where Arizona, Colorado, New Mexico, and Utah meet. Old aerial photos had traced roads extending from some sites. But a 2017 paper in Advances in Archaeological Practice revealed previously unknown roads.

For this project, Anna Sofaer, an archaeo-astronomer who heads the nonprofit Solstice Project in Santa Fe, collaborated with Richard Friedman and Robert Weiner, who specialize in lidar, a technology that uses laser pulses from an airplane to reveal fine features on the landscape. Their analysis of three small areas near the park detected previously undocumented road segments and suggested that hundreds, perhaps thousands, of ancient roadways traverse the San Juan Basin. The pilot study "told us what the potential would be for the whole Chaco region," Sofaer says. "Now we know that each of these great houses has spokes of roads [around it]."

The lidar work also "helps us understand just how much effort went into creating what we think of as this greater Chacoan world," adds Friedman, a Chaco expert and geographic information systems instructor at San Juan College in Farmington, New Mexico. "A 30-foot [9-meter] road … took a lot of labor just to create."

Filling in a road map

Aerial and historic photos have revealed some ancient roads in the Chacoan region, especially near the national park (mapped below), but lidar analysis uncovered at least 5 kilometers of previously unknown thoroughfares, implying a far more extensive network.

CREDITS: (MAP) A. CUADRA/SCIENCE; (DATA) BUREAU OF LAND MANAGEMENT

Many of the roads are more than twice as wide as modern two-lane thoroughfares, even though Ancient Puebloans had no wheeled transportation or beasts of burden. Some roads lead to Chaco Canyon, the epicenter of Ancient Puebloan society and now the heart of the national park. Others seem to lead nowhere. When Sofaer and colleagues explored one newly identified road from the ground, they found a mix of sherds from different pots strewn along the roadbed, lending credence to the theory that this road, at least, was for ceremonial use.

Few roads outside the park are protected. "Historically what was protected was the large building sites and the boundary around them" in the national park, Sofaer explains. "The question is how we protect the areas between the sites."

Although companies have pumped oil and gas from the basin for a century, development only recently spread into the Chaco area, after advances in directional drilling and hydraulic fracturing allowed companies to coax oil and gas from the previously impenetrable Mancos shale formation underneath the region. In March, BLM planned to offer 26 parcels for lease to oil and gas companies. One grazes the periphery of a 16-kilometer-wide temporary buffer that former President Barack Obama's administration imposed around the park; another parcel lies near a site along the Great North Road, a 9-meter-wide thoroughfare that leads 50 kilometers straight north from Chaco Canyon. After a Navajo group and environmental groups protested the leases, Secretary of the Interior Ryan Zinke suspended the sale.

On 23 April, however, Judge James Browning of the U.S. District Court for the District of New Mexico issued a ruling that may have implications for those shelved parcels. In 2015, environmental groups had sued BLM, arguing that it failed to protect cultural sites when approving drilling permits in the Chaco area. In the new ruling, Browning disagreed. He wrote that BLM only needed to survey the immediate area where the well would be drilled and that it had demonstrated that "Chaco Park and its satellites are outside of the wells' APEs [areas of potential effect]."

That decision could bring the 26 suspended parcels back into play, says Kyle Tisdel, an attorney with the Taos, New Mexico, office of the Western Environmental Law Center, which brought the suit on behalf of the groups. "I can imagine the judge's ruling emboldening the [BLM] field office to further prioritize oil and gas," he says. Meanwhile, New Mexico senators and indigenous groups are pressing BLM to place a moratorium on energy development in the area until the agency updates its 2003 resource management plan, which was crafted before heightened industry interest in the Mancos shale.

Zach Stone, a spokesperson for BLM's Farmington field office, says energy development has actually contributed to the archaeological record. He notes that BLM must conduct cultural surveys before drilling on a leased parcel can begin. "A lot of these sites would never have been found without oil and gas development, because we have to go out and look for them" before drilling starts, he said. BLM recently commissioned lidar surveys for the area around the park but has analyzed little of the data so far, and it's unclear whether the data will inform the new management plan.

Friedman says BLM's ground surveys may miss the subtle signs of ancient roads. Sofaer estimates that as many as 80% of roads are still undocumented, and she fears that without costly lidar analysis, they never will be. Her team's $600,000 project to conduct a lidar survey of Chacoan lands in southeastern Utah failed to find funding. In March, BLM leased several parcels there, at least one of which abuts a Chacoan great house and, perhaps, roads that have yet to be found. "This [development] is happening just as we're discovering the larger landscape," she says.

Friedman is taking matters into his own hands: He recently acquired BLM's full lidar data set and will begin combing it for more roads in the area around the park. "That's in my spare time," he says.