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Museum of Anthropology Granite Point (45WT41)

Geologic History and Natural Environment

The region surrounding Granite Point was formed through deep basaltic lava flows which were later overlaid with loess. The Granite Point locality is described as resting atop a “prominent granodiorite spur of pre-Miocene age jutting out above the Snake River below the Wawawai Canyon” (Reid 1991), located approximately two miles downstream from the historic town of Wawawai. Native vegetation was a semi-arid steppe habitat with various grasses. The rain shadow effect from the Cascade mountain range has created a modern climate with comparatively mild winters and cool summers. The region receives an average of 20 inches of precipitation annually, primarily in the form of snow during the winter months, with less annual temperature variation than may be expected for the region.

 

Geologic Sequence

Sediment stratigraphy provides a chronology of natural and human activity at the site. On its own, sediment stratigraphy is only able to provide a relative chronology of events.  Radiocarbon dating of remains collected from sediment layers and the identification of specific events that occurred at a known time, like a volcanic eruption, can provide a temporal sequence for the stratigraphic chronology. Leonhardy (1970:1) stated that the purpose of the salvage excavation at Granite Point was to “document the existence of separate and discrete archaeological units in a site typical of the Lower Snake River Region of the Southern Plateau”. At the time, this emphasis on establishing a temporal and cultural sequence at individual sites was a common research trend among American archaeologists. These individual sequences could then feed into the creation of regional sequences.

In order to create a comprehensive timeline, the 1967 excavation supplemented the sediment stratigraphy recorded from the excavation units at the site with the stratigraphic records of 25 additional test pits excavated specifically for their stratigraphy. At the conclusion of the field season, the field data collected at these separate exposures were used to construct a tentative geological sequence. Unfortunately, this tentative sequence was unable to fully account for some stratigraphic unconformities and correlations, requiring additional work during the 1968 excavation to complete Granite Point’s geological chronology. The 1968 excavation worked to rectify the geological sequence proposed in 1967 through the correlation of 7 key stratigraphic units: Area A, Area B, Area C, Stratigraphic Section 1, Stratigraphic Section 2, Stratigraphic Section 3, Stratigraphic Section 7. These stratigraphic correlations were made based on the sediment’s physical characteristics, relative topography and stratigraphic position and elevation, relationship to the volcanic ash horizon marker, and relationship to the soil stratigraphy horizon markers. Efforts in the field were followed by additional laboratory sediment analysis that enabled the formation of a generalized reconstruction of the geological sequence at Granite Point.

Geologic Sequence Basic TextureMax. Thickness
Historic Deposits/Modern Soil
Thin Colluvium Fine sandy loam to course sand, grayish brown to dark brown20cm
Post-Ash Aeolian Sands Very fine to medium sandy loam, pale brown to dark grayish brown1.9cm
Later FloodplainsVery fine sandy loam, light brownish gray1.6m
Pale LoessVery fine sand to silt loam, light gray to pale brown1.25m
Volcanic AshVery fine sand to silt, light gray to white65cm
Pre-Ash Aeolian SandsVery fine sandy loam, very dark brown60cm
Early FloodplainVery fine sandy to silt loam, yellowish brown to dark brown>2m
Gravel Bar and Alluvial FansBasalt boulder and light brownish gray granule; silt loam
Boulder GravelSubangular basalt boulders as much as one meter maximum in diameter
Correlation of Stratigraphic Units in Seven Key Stratigraphic Sections (Leonhardy 1970, Fig. 27)
Correlation of Stratigraphic Units in Seven Key Stratigraphic Sections (Leonhardy 1970, Fig. 27)

 

 

Radiocarbon Dating

Six samples were submitted for radiocarbon dating. Adequate samples of charcoal were not available in the earlier deposits and shell was used in its absence. Unfortunately, all of the shell dates are aberrant or contradictory.

AreaStratumAssociationC-14 DatesSample Type Sample
AStratum 1Feature 32955 +/- 155 B.PCharcoalWSU-666
AStratum 3CFeature 362,440 +/- 170 B.P.CharcoalWSU-667
B60-80cm below Stratum 2 - Stratum 3 boundary3,075 +/- 160 B.PCharcoalWSU-665
A20cm below Stratum5 - Stratum6 boundaryFeature 335,145 +/- 200 B.P.Shell (Margaritifera falcata)WSU-668*
AStratum5 - Stratum 6 boundary5,980 +/- 190 B.P.Shell (Margaritifera falcata)WSU-529*
C Upper 20cm of cobble gravelUnit 114,100 +/- 1,160 B.P.Shell (Margaritifera falcata)WSU-870**

Radiocarbon Dates from 45WT41 (Leonhardy 1970, Table 24)

* WSU-668 was submitted as a check on WSU-529, with which it conflicts. WSU-668 is considered the more reasonable date.

** Date considered to be far too early and conflicts with the geological estimate of the age of the gravels. This date was discarded.