CA-MNT-1918
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Soils and Stratigraphy
The natural soils in the site area are classified as psamments and fluvents (Soil Conservation Service 1978). These are areas of stratified sandy, gravelly, and cobbly sediments on flood plains which is an accurate characterization of the soils underlying the cultural deposit which clearly represented high-energy alluvial deposit. Given the size of the gravels and cobbles in this soil, and their distance from present-day Jolon Creek, they almost certainly dates to the Pleistocene. Even during the wettest years, flow in Jolon or Murry Creek would not be strong enough to account for the large alluvial cobbles and gravels found at this location today.
As with at CA-MNT-910, this site was originally identified as a lithic scatter,
but subsurface investigations showed it to be a midden albeit one with very
poor organic preservation. The midden (stratum I) was extremely homogeneous
and extended to an average depth of 70 cm. It was marked by a very dark grayish
brown sandy silt with rounded to subangular gravels. Minor variation in the
frequency of fist-sized rounded and occasionally fractured cobbles suggested
two minor variants of this basic soil (strata Ia and Ib). Stratum Ia which extended
from the surface to approximately 20 cm had only occasional fist-sized or larger
cobbles. Below 20 cm, fist-sized and larger cobbles were slightly more abundant.
Beneath the midden was a sterile brown silty sand with a high percentage of
rounded to subangular gravels and a moderate number of fist-sized and slightly
larger cobbles.
A total of 35 soil samples was collected from a systematic sample of horizontal
(STU) and vertical (unit) proveniences. These were was analyzed for pH using
a Poly-D pH reagent kit from the California Polytechnic State University Soil
Science Department, and the resulting values show strong if not significant
patterning. The overall range of values was from 5.2 to 6.8 or medium to very
slightly acidic, although only one reading of 6.8 was obtained and all other
readings were 6.6 or below. The mean value for the 35 readings was 6.14 which
signifies medium acidity, but this more acidic than any soil at any of the other
investigated sites. Patterning was also apparent in the distribution of pH values
across the site area. In general, pH readings from near surface depths on the
periphery of the site tended to be very low (less than 6.0), while readings
in the central site area were generally above 6.0. The readings showed no significant
variation with depth, however, as all of the units in the central portion of
the site produced values between 6.3 and 6.6. Overall, the pH of this site suggests
medium acidity which provides a poor environment for organic preservation. The
higher pH values in the central portion of the midden suggested that materials
deposited in this area prehistorically had some affect upon soil acidity- slightly
offsetting the natural acidity. As discussed in more detail below, the near
absence of bone and shell from the midden is almost certainly a reflection of
soil acidity and the age of the occupation. PH values were used to help define
the limits of the midden at CA-MNT-1918 as the area producing the most alkaline
values seemed to correspond with the greatest concentration of cultrural materials
and darkest soil.
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| CA-MNT-1918, sidewall profile, Units 3 and 7 |
Soil Conservation Service
1978 Soil Survey of Monterey County, California. United States Department of
Agriculture in cooperation with the University of California Agriculture Experiment
Station. United States Government Printing Office, Washington D.C.