Ancient Native American mining areas found in Montana
May 4, 1997
A team of University of Colorado at Boulder researchers has
combined a set of remote-sensing techniques to pinpoint a series of
eight previously unknown Paleo-Indian quarries in Montana dating back as
far as 10,000 years.
Led by anthropology doctoral student Thomas Carr, the team used
satellite images, aerial photographs and ground-based geophysics to develop
a new method for locating ancient Native American mining pits from space. The
quarries, the largest of which is about 200 meters on a side, were used by
ancient North Americans to obtain a quartz-like material known as chert for
toolmaking.
A paper on the subject by Carr and research associate Mort Turner
of CU-Boulder's Institute of Arctic and Alpine Research was presented at a
recent conference at the University of Pennsylvania Museum of Archaeology
and Anthropology in Philadelphia.
"It looks like the heaviest use of these
particular quarries came
during the Paleo-Indian and
Archaic Periods, from about 10,000 years ago
to
about 5,000 years ago."
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The researchers used aerial photographs, geologic maps and ground
tests to develop "spectral classes" characterizing 12 distinct geologic and
vegetation types found in the Horse Prairie Valley study area in southwest
Montana. Their data included electromagnetic measurements of soil
conductivity from a known Indian quarry in the area called the South
Everson Creek site, which is characterized by "altered bedrock" containing
veins of chert and an adjacent area of soil disturbed by quarry activity,
said Carr.
The team ran the data on a computer software package known as ENVI
developed jointly by Research Systems Inc. of Boulder and CU's Center for
the Study of Earth from Space. The software compared nearly 1 million
30-meter-by-30-meter pixels, or picture elements, from a 1985 Landsat
satellite image of the area to each of the 12 spectral classes, identifying
the most likely matches.
The researchers speculated that pixels of altered bedrock located
next to pixels of disturbed soil like those at South Everson Creek would be
the most likely places to find ancient quarries. Out of 12 possible sites
identified by the team in the 800-square-mile research area, eight were
confirmed to be ancient Indian quarries during a subsequent ground survey
using GPS satellite receivers for accuracy, Carr said.
The four other sites identified as possible Indian quarries turned
out to be naturally eroding ridges containing large amounts of opal-based
silicates similar to the chalcedony-based chert from Everson Creek. "The
four failures actually provided the strongest evidence for why our
technique worked," said Carr.
Although the spectral classes developed by the CU team are specific
to Montana's Horse Prairie Valley, researchers could conceivably use the
technology in many other regions of the world to pinpoint ancient quarrying
activity, he said.
While Landsat satellites "see" in six spectral bands -- three in
visible light bands and three in the infrared -- next-generation satellites
will see in more than 200 spectral bands, making future searches "much more
sophisticated," said Carr.
As part of his doctoral thesis, Carr plans to use a portable
spectrometer to analyze the chemical signatures of individual artifacts
from the Horse Prairie Valley region, which may allow him to track known
artifacts back to specific quarries.
It looks like the heaviest use of these particular quarries came
during the Paleo-Indian and Archaic Periods, from about 10,000 years ago to
about 5,000 years ago," Carr said. "My suspicion is that the South Everson
Creek quarry was heavily used during that period, and an overflow
population during the Archaic period caused some of the people to begin
working the outlying quarries."
Indian artifacts made from South Everson Creek chert have turned up
200 to 300 miles away, including the Snake River Valley of Idaho, the
Columbia River Basin and the Northern Great Plains. The project should
shed new light on Native American settlement, trading and migration
patterns in the region, he said.
Special thanks to the University of Colorado.
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