Pipeline to the Past: A Modern Project Leads to Prehistoric Gold

The Express Pipeline Project, initiated in 1993 and still under construction, will be 800 miles long when it's finished, extending from Hardesty, Alberta, Canada, to Casper, Wyoming. Its 24-inch pipe is distributing oil to existing pipes leading to communities in the Rocky Mountain states and the Midwest.

A map showing the length of the Express Pipeline Project with the Rocky Mountains visible to its west.

Because the Express Pipeline was the first major project to be constructed along the east side of the Rocky Mountains, Federal law required an assessment of archaeological and historic properties - "cultural resources" - potentially located in the path of construction. For Mike and his team, this legal requirement has afforded a unique opportunity to investigate prehistoric American life in this portion of the country. Archaeological excavations began in late 1995. So far, the team has performed excavations of 39 archaeological sites along the pipeline corridor, though this represents only a small percentage of the 487 prehistoric and historic sites documented in Montana and Wyoming over the life of the project to date. (If a test unit revealed that artifacts or features of a site were not in-place, i.e., that they'd been moved from their original location or otherwise disturbed, the site was documented, but not investigated further.) The U.S. portion of the pipeline corridor has been divided into six ecological zones - representing different physiographic basins - to help the archaeologists compare living habits of ancient peoples over the length of the corridor.

Digging for Evidence

In advance of any excavation work, archaeologists prepare a "Historic Properties Treatment Plan (HPTP)," which outlines the physical/cultural context of an area; puts forth the Research Design identifying the questions to be answered through inventory and excavation; and addresses specific localities for investigation, on the basis of existing information.

Archaeologists aim to discover buried sites before construction activities reach and possibly damage them. But however diligently they may dig test pits, use remote sensing techniques and study existing research, sometimes sites are still only identified when construction equipment unearths clues. For this reason, construction activities themselves are methodically monitored by archaeologists in the course of their work. Out of the 39 archaeological sites excavated in association with the pipeline, for example, 13 were identified during monitoring of construction activities.

Archaeologists also use remote-sensing techniques to pinpoint the locations of sites, and to guide them in delineating proposed areas of excavation. These techniques enable scientists at the ground's surface to "see" what is located beneath. At Site 48NA2526, ground-penetrating radar (GPR) was tested as a means to determine the location of underground features. Though GPR had not worked well for some previous excavations along the pipeline corridor, the soils at 48NA2526 turned out to be well-suited to this technique, wherein radar waves are directed into the ground, bounce back from soil horizons, and are read by an on-site computer at the surface. The resulting profile, or log, displays the soil layers and any included disturbances or anomalies that may indicate the presence of a site.

An IMAC technician running ground-penetrating radar.

Mike's team primarily used the results of test units - small excavations designed to provide clues on the extent and importance of a site - to guide them in delineating the proposed overall excavation at 48NA2526, whose total area is 90 square meters. This size is about average for the excavations performed along the pipeline corridor.

How is Excavation Accomplished?

Mike and his team take great care not to disturb the resources at any site, and 48NA2526 is no exception. Shovels and hand tools (e.g., trowels, soft brushes) are the only implements used for excavation. Every effort is made to locate and map artifacts in place, or, to use the technical term, in situ. Often, this is not possible because the artifacts are too small or too deeply embedded in the soil matrix. In those cases, box sifters suspended from long-legged tripods are used to gently sort excavated materials, and all finds are painstakingly identified, catalogued, and mapped within the site.

So What Have They Found So Far?

Two sites excavated by Mike and his team in Washakie County, northwest of the Natrona County site, were prehistoric camps dating to 5,000 - 3,000 BP (before present). (Radiocarbon dating was performed on wood samples from the sites to establish the sites' age range. See our previous Resource Explorer feature for a brief explanation of this technique.) The Natrona site dates from the same period, based on radiocarbon dating of one of its wood samples.

Materials recovered from both the Washakie and Natrona sites include:

- stone flakes that are remnants of the manufacture of stone tools;

- heat-altered quartzite, probably used to ring circular hearths;

- flake tools, which are stone flakes purposely shaped into tools;

- manos and metates, which are stone food-grinding instruments;

- other types of groundstones, used to grind food, minerals and wood;

- ceramic sherds, which are remnants of fired clay containers;

- projectile points made of chert;

- sewing awls made of bone; and

- animal-bone fragments.

These artifacts, associated with open camp living areas, tend to be buried fairly shallowly at these sites, in the soil layers located 50 to 110 cm below the surface.

A view of a Washakie County excavation, showing ( clockwise from lower left): a housepit containing metates (stones at edge of depression), a second housepit (middle left of photo), circular hearths and storage basins (lower center of photo), and a third housepit (upper center of photo).

Non-artifact discoveries at these sites include relatively large depressions that formed the bases of prehistoric dwellings called pithouses, and smaller depressions (basins), which were used for domestic storage. The team expected to find few shreds of organic pithouse components, such as the wood and plant fibers usually used on walls and roofs, since these materials generally decay in place. Sometimes, evidence of these wall and roof components is absent altogether, since it was common for prehistoric occupants to remove them for re-use at another site. Since in some cases one housepit was superimposed upon another at Site 48NA2526, Mike and his team believe that there were actually two periods of human occupation at this site.

A Lasting Legacy

The team removes any artifacts and "feature fill" (soil and other materials found in housepits and basins) for examination in the laboratory. There, the fill is mixed with water and sifted through progressively finer screens to remove any items of interest, such as small seeds and stone flakes. After all examinations are complete and data compiled, the artifacts are stored at the University of Wyoming curation facility and used for public display or made available to future researchers.

After documentation, pits, basins and hearths are backfilled with the soils excavated from the site. By the time the team is through with an excavation, they will have collected so much information that not only can they thoroughly map the site, they can even produce 3-dimensional graphics showing the discovery depth of each artifact or feature.

What About the Involvement of Modern Native Americans?

Representatives of many tribes of contemporary Native Americans, including Shoshone, Cheyenne, Crow, and Blackfoot, were involved from the very beginning of the Express Pipeline Project. Once the initial archaeological inventory was done, these representatives were presented with the findings and asked for their input. An ethnographer - a specialist in descriptive anthropology - was contracted by BLM to accompany tribal representatives to the areas of concern to them. Then, in several cases, mostly involving cairns that marked possible human burial sites, the pipeline's course was re-routed to avoid disturbance of these sensitive areas.

What About the Other Sites, in the Pipeline's Path? Are They Just Ruined?

Generally, the pipeline trench only goes through part of any given site, so the underground features at that site are not entirely lost.

When Will the Project Be Complete?

The pipeline is scheduled for completion in late 1997, and the final archaeological report is expected to be prepared by April 1999.