Archaeological inspection and monitoring of the MAPL-WEP Pipeline in Sweetwater and Uinta Counties, Wyoming

Feature 1 visible in the pipeline trench at Site 48SW16725.

Feature 1 visible in the pipeline trench at Site 48SW16725.

Between September 2007 and July 2008, the CRA office in Longmont, Colorado, completed an archaeological inspection and monitoring project in Wyoming. CRA was contracted by Enterprise Products, LLC, to conduct an open trench inspection and monitoring along Segment 6 of the MidAmerican Pipeline Company-Western Expansion Project (MAPL-WEP) Pipeline in Sweetwater and Uinta Counties, Wyoming. The work was conducted in compliance with a Memorandum of Agreement between MidAmerican Pipeline Company, the Wyoming BLM, and the Wyoming State Historic Preservation Office dated June 6, 2006.

During the project numerous sites were located, and a variety of mitigative measures were implemented along the pipeline corridor. The mitigative measures included an erosional treatment plan for Site 48SW15859, protective fencing and monitoring for the Overland Trail and the Rock Springs to Vernal Wagon Road, and limited data recovery at Site 48SW1672 and the Maxon Ranch Site (48SW2590).

Features at the Maxon Ranch Site

Investigatory map of the Maxon Ranch Site showing 2 investigation areas in relation to previous workings.

Investigatory map of the Maxon Ranch Site showing 2 investigation areas in relation to previous workings.

At the Maxon Ranch site (48SW2590) several new features were discovered. A data recovery plan was created. Some of the tested features were near the surface, and testing was needed to determine if they maintained integrity. Others were found at a depth of up to 1.5 meters and required testing to determine their nature. Auger probes were excavated all around the trench feature to determine the extent of the identified dark strata. These probes contained no artifacts, though each probe encountered enough buried charcoal to hint at a buried cultural stratum.

Artifacts discovered

Eight of the fourteen features located in the right-of-way and Trench Feature 1 were tested. Artifacts were recovered from excavations at Maxon Ranch, including 124 flakes, 2 bifaces, 1 tested cobble, and 80 pieces of bone. Eighty five percent of the lithics recovered were located in CRA investigation Area 2. In CRA Investigation Area 1, there was a dispersed lithic scatter that contained very few flakes and no discernable cultural horizons. Three radiocarbon dates were recovered from the site, which placed the occupations between 7000 and 2755 years before present. Paleobotanical analysis recovered ancient seeds from the mustard, grass, and sedge families.

A Feature Can Tell a Story

The investigations at Site 48SW16725 focused entirely around Feature 1, a large basin-shaped feature measuring 7.3 meters from end to end and visible on both walls of the pipeline trench. The site was initially recommended as potentially eligible for nomination to the NRHP since the feature had the dimensions of an Archaic-age house pit with radiocarbon dates that were much older. Collaboration by Linda Scott Cummings at Paleoresearch proved the feature to be between 12,200 and 11,200 years old. These dates put the feature into the Folsom era, where no semi-subterranean dwelling like a pit house has ever been recorded.

East wall profile showing 4 buried A horizons and the near black fill of Feature 1.

East wall profile showing 4 buried A horizons and the near black fill of Feature 1.

During the course of investigation it was determined that the feature was not cultural. Bill Eckerle at Western Geoarch conducted a geomorphic analysis that proved the feature to be a small pond or marsh created by a water saturated hillside slumping to create a dam. This led to the site being sampled to document the paleoenvironmental conditions of the Folsom era. Paleobotanical remains recovered from the feature showed a climate during deposition that was significantly wetter than it is today with members of the rose, sunflower, snowberry, and buckwheat families present in an area that is mostly sagebrush and grass today.

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