Mingus Mountain Substation Site Data Recovery Project

Just up the road from historic Jerome in central Arizona, the future meets the past at the APS Mingus Mountain Substation. Nestled in the Prescott National Forest (PNF), the substation quietly hums along converting 69kV to 12kV electricity for distribution to homes and businesses. At peak load the substation exceeded the capacity of the existing transformer and needed to be upgraded and expanded to meet current and future demands. There was one small hitch, however—the substation was built on and in the middle of an archaeological site.

Mingus Substation was built in the mid-1950s before historic preservation laws now in place were created. In the intervening years, the substation underwent routine maintenance but largely sat undisturbed among the ponderosa and juniper atop Mingus Mountain. In 2003 an archaeological survey of the surrounding forest identified several archaeological sites in the area. One of these sites was located under the substation and surrounding it on all sides. The site was documented but was otherwise left alone in its current state of impact. Once it was realized that the substation would require expansion, the site became a factor. The Forest Service and Arizona State Historic Preservation Office (SHPO) had determined the site to be eligible for listing on the National Register of Historic Places. Proposed improvements to the substation included ground-disturbing activities outside the already disturbed substation footprint, such as expanding the perimeter fence and replacing wooden power poles with 50-foot steel poles. The Register-eligible status of the site warranted mitigation of adverse effects from the proposed substation expansion activities to what remained of the site.

The PNF and SHPO determined that the best way to treat the site was through archaeological investigation prior to the planned substation expansion. In 2006 EnviroSystems Management, Inc. developed a Historic Property Treatment Plan (HPTP) for the site in consultation with the PNF, SHPO, the Fort McDowell Indian Community, Hopi Tribe, Hualapai Tribe, Tonto Apache, Yavapai-Apache Nation, and Yavapai-Prescott Indian Tribe. A Memorandum of Agreement (MOA) served to implement the treatment plan. APS and four of the tribes that voiced interest in the project were given the opportunity to sign the MOA as concurring parties. Following the successful development of the HPTP and MOA, EnviroSystems was contracted to carry out the investigations at the site.

During May 2007 a crew of EnviroSystems archaeologists conducted fieldwork at the substation site. The EnviroSystems team did substantial work before a single shovel load of dirt was moved. We first investigated the artifacts found spread across the site’s surface. Based on the information recorded when the Mingus Mt. Sub Site was originally documented, we knew it had at least two archaeological features amidst a variety of prehistoric and historic artifacts. A mapping grid was established across to keep track of where artifacts were found. Artifacts were collected in those areas most likely to be impacted by the substation expansion, while items that were farther away were analyzed in the field and left in place.

After the surface materials were cataloged, archaeologists begin digging and excavated a series of test units, large square holes about 3 feet on each side. Dirt from these units was screened to capture and find artifacts hidden in the sediment. Most test units were dug in areas where surface artifacts had been collected. Following excavation, these holes were backfilled and the archaeologists began excavating the two known features.

The features consisted of a roasting pit and an oval, rock-encircled surface structure. The roaster was a circular, 18-inch-deep hole about 7.5 feet in diameter, that was filled with sharp pieces of fire-cracked rock surrounded by dark charcoal-rich sediment. Botanical samples collected from the pit failed to indicate what had been cooked there. Comparing this to other early historic roasting pits, it might have been used to roast the hearts of agave plants. The rock-outlined structure appeared to be the remains of a house similar to a wickiup that would have had a brush- or hide-covered branch superstructure held in place by the stones along the base of the wall. The structure’s exterior measures 14.5 feet long and just over 13 feet wide.

Mingus_PitOval rock-outlined house excavated at the Mingus Substation site.


Following completion of the fieldwork, EnviroSystems took all field notes, maps, photographs, and collected artifacts back to our laboratory in Flagstaff for processing and analysis. A preliminary report was prepared documenting our findings, and upon approval, allowed substation construction to proceed.

Among the important discoveries, we determined that the site was occupied or visited repeatedly throughout both prehistoric and historic times. Most of the prehistoric artifacts consisted of debris generated during the production or sharpening of flaked stone tools like arrowheads and spear dart points. These projectile points ranged from several thousands of years old to only a few hundred years. Analysis of obsidian flaked stone revealed that most of the obsidian found at the site was from Government Mountain west of Flagstaff, nearly 100 miles to the north.

Mingus_PointsProjectile points/point fragments found during archaeological investigations at the Mingus Substation Site.


In addition to the flaked stone a few pieces of broken pottery were discovered. The pottery indicated an occupation at least once sometime between A.D. 800-1400. Although not numerous, the types of ceramics showed ties to both the Southern Sinagua to the east in the Verde Valley and the Prescott Culture to the west.

A piece of charcoal from the roasting pit was radiocarbon dated and found to be between 200 and 500 years old. The roaster and structure are similar to those used historically by Yavapai and Paiute peoples. Combined with the fact that the site lies within the historical geographic range of the Yavapai people, the features strongly suggest an A.D. 1500-1800 Yavapai occupation.

Evidence indicates that the structure was later reused sometime between 1880 and 1915. Clothing fasteners, glass bottle shards, nails, ammunition cartridge cases, and cans dating to this time period were found both inside the structure and around it. A second historic component dating to the 1940s-1950s is represented by a light surface scatter of cans, glass container fragments, and an ammunition cartridge case. These items are probably trash left behind by campers or possibly the APS workers who originally built the substation. Both historic time components are overlain with a light scatter of more recent (1960s-present) artifacts representing camping and roadside trash, in addition to ad-hoc rock alignments and rock-lined campfire hearths associated with camping activity.

The full data recovery report describing the investigations and findings at the Mingus Mountain Substation Site is complete. This APS-funded project has helped to preserve the information from the past found at the site, while simultaneously allowing the company to move forward to meet the power needs of the immediate future in the region.