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dsolproc.doc	5/1/95	

SAMPLING AND LABORATORY PROCEDURES AND MATHEMATICAL EQUATIONS 
FOR SOILS AT DUST-TRAP SITES IN SOUTHERN NEVADA AND CALIFORNIA

file dsolloc.xls
Named soil localities in this file are taken from previously published studies at sites where 
we had placed dust traps in 1984.  Numbered soil localities correspond to dust-trap sites where 
soils were described and sampled after the traps were in place, mainly in 1988 and 1989.  
References cited in the file are listed at the end of this document.

file dsoldes.xls
Numbered profiles (11H, 11P, etc.) were sampled specifically for this study.  Two profiles 
from San Felipe Creek (SF1 and SF3) are unpublished data contributed by Tom Rockwell (San 
Diego State University).   Methods for the descriptions of all of the soils were the same.
Soil profiles were described and sampled in many places where no previous soil studies 
had been done.  In each area, two alluvial-fan surfaces were selected that were thought to be late 
Pleistocene and middle to late Holocene in age by comparison of surface characteristics such as 
pavement, varnish, and preservation of depositional topography to those of dated surfaces from 
previous studies in the region (for example, McFadden and others, 1989; Reheis and others, 
1993.i.Reheis, 1992;).  One soil profile was described and sampled on each surface using either 
fresh stream cuts or hand-dug pits.  Soil descriptions and horizon names followed Guthrie and 
Witty (1982) and Birkeland (1984).  Stages of CaCO3 , silica, and salt follow definitions of Gile 
and others (1966), Taylor (1986), and Reheis (1987), respectively. 

file dsindprn.xls
The soil development index (Harden, 1982) provides a means of quantifying field 
properties of soils in order to compare their development.  Index values of field properties 
including rubification, melanization, paling, lightening, texture, structure, dry consistence, pH 
decrease, pH increase, and carbonate (Harden, 1982; Reheis, 1987; Harden and others, 1991b) are 
calculated for each profile using a spreadsheet template (Taylor, 1988).  Normalized values of 
these properties are multiplied by horizon thickness to obtain the horizon index; the horizon values 
within a profile are summed to obtain the profile index.  Horizon and profile index values are given 
for all of the soils sampled for this study.
The ages of the soils sampled for this study (11H, 11P, etc.) were estimated from field 
morphologic data using the soil development index.  The index values were compared with values 
for soils of known age that formed under similar conditions of climate and, where possible, parent 
material (Taylor, 1986.i.Taylor, 1986;; Reheis and others, 1989.i.Reheis and others, 1989;, 
1992.i.Reheis and others, 1992;; Harden and others, 1991a; Slate, 1992.i.Slate, 1992;), and 
"best" ages and age ranges were assigned to the soil profiles.  Harden and others (1991b).i.Harden 
and others (1991);, using a statistically based version of this technique in a study of soil 
chronosequences in the southern Great Basin (some of the sites used in this study), suggested that 
average rates of most soil-development parameters within this area are precise to about a factor of 
two and that, at least for Holocene soils, estimated ages derived from these rates might be accurate 
within about a factor of two or three.
Sites that provided soil ages for the study were the Whipple Mountains (McFadden, 1982), 
the Fortymile Wash-Yucca Wash area (henceforth referred to as the Fortymile Wash area; Taylor, 
1986), Silver Lake (Reheis and others, 1989), Kyle Canyon (Sowers and others, 1988), the Cima 
fans (Harden and others, 1991b), Wilson Creek (Harden and Matti, 1989), and the Coyote 
Mountains (Goodmacher and Rockwell, 1990).  Some ages were based on various methods of 
radiometric dating of deposits and soils, and others were based on correlation of soil properties to 
those of soils at other dated sites using the soil development index of Harden (1982).i.Harden 
(1982); and modifications to the index (Reheis, 1987; Taylor, 1988; Harden and others, 1991b).

file dsolab.xls
Most of the samples were analyzed using standard laboratory techniques (Singer and 
Janitzky, 1986.i.Singer and Janitzky, 1986;) for grain size, CaCO3 and organic-matter content, 
pH, and salt content, except that the total salt equations in Singer and Janitzky, published with an 
error, were corrected using a multiplication factor of 0.32 rather than 320.  pH for the soils 
sampled specifically for this study was measured in 1:1 H2O, whereas the pH for soils from other 
sources was measured using CaCl2.  Some other analytical techniques for the Kyle Canyon soils 
were also different because the soils formed in carbonate-rich alluvium.  The contents of CaCO3 
and silt plus clay reported in this table were measured using a combination of chemical, 
microscopic, and photographic techniques (Sowers, 1988; Reheis et al., 1992) and are the 
amounts of pedogenic (non-parent material) carbonate and silt plus clay, not total amounts.  In 
addition, the salt content reported for Kyle Canyon soils is for gypsum only, not total salt.  
Data for Wilson Creek (WC) soils is unpublished data of J.W. Harden; data for Cima fan 
soils (CV) is unpublished data of E.M. Taylor, J.W. Harden, and L.D. McFadden; data for Silver 
Lake (SL) soils is unpublished data of M.C. Reheis, J.W. Harden, and L.D. McFadden; data for 
Kyle Canyon (KC) soils is from Reheis and others (1992); and data for Coyote Mountains (FC 
and AC) soils is unpublished data of Jonathan Goodmacher (also Goodmacher and Rockwell, 
1990) except that salt values are different owing to an error in the original calculations (see first 
sentence of this section).

file dsolpw.xls
The bulk density for each soil horizon, if not measured by previous reports using either the 
paraffin-clod method or the excavation technique, was estimated from particle size and the contents 
of gravel and organic matter using the technique of Rawls (1983).i.Rawls (1983);.
Profile weights (g/cm2/soil column) were calculated for pedogenic silt, clay, CaCO3, and 
salt (where possible).  The contents (percentages) of these components in each horizon of a soil 
were subtracted from the contents estimated to have been present in the parent material (method of 
Machette, 1985), multiplied by the bulk density of the less-than-2mm fraction and by horizon 
thickness, and then summed for the soil.  At most sites, the parent material consisted of alluvial-fan 
deposits, commonly debris flows.  Debris flows are usually unsorted and unbedded, so the content 
of silt, clay, and CaCO3 in a C horizon formed in these deposits was assumed to be representative 
of that originally present in the other horizons.  For soils at Wilson Creek that formed in fluvial 
deposits potentially containing fine-grained overbank sediment (Harden and Matti, 1989), amounts 
of silt and clay in the parent material of the A and B horizons were estimated to be greater than 
those in the C horizons.  Basalt flows were assumed to contain no silt, clay, or CaCO3 when 
deposited.
In this study, we assume that the dust component of soils is pedogenic, not parent material, 
and that all silt, clay, and CaCO3 present in greater proportions in a soil than in the parent material 
is pedogenic material and ultimately derived from dust.  Soils that formed in carbonate alluvium are 
one exception; they contain abundant CaCO3 derived from solution of the parent material (Sowers, 
1985; Reheis and others, 1992).  The major-oxide composition and clay mineralogy of the dust 
and soil horizons support this assumption.  Previous work in the study area (McFadden, 1982; 
McFadden and others, 1986; Taylor, 1986; Reheis and others, 1989, 1992) indicated little 
chemical weathering in soils of this age.  Soils that are more than about 100,000 years old or that 
formed in semiarid to subhumid climates have likely been chemically weathered.  However, much 
of the silt, clay, and CaCO3 in older aridic soils is likely to be of eolian origin, in part transformed 
into other minerals or grain sizes by chemical or physical processes.
Profile weights for Coyote Mountains soils (AC and FC) were recalculated from original 
data because profile weights given in Goodmacher and Rockwell (1990) did not account for 
parent-material values.

file dsolox.xls
Major-element contents for the Kyle Canyon and Silver Lake soils were measured using 
wavelength-dispersive X-ray fluorescence spectroscopy (XRF) and zirconium content using 
energy-dispersive XRF (Baedecker, 1987) on the less-than-2mm fraction including CaCO3.  
Oxide percentages were recalculated to 100% to correct for the amount of water and other volatiles 
not measured.  For the Wilson Creek soils, only Fe2O3, K2O, CaO, TiO2, MnO, and ZrO2 were 
measured using energy-dispersive XRF.  In order to compare the soil analyses with those of 
nearby dust samples, which did not include Ca from CaCO3, the contents of major oxides in the 
soil samples from Kyle Canyon and Silver Lake were recalculated on a CaCO3-free basis (Wilson 
Creek soils contained no CaCO3).  Values for Silver Lake (SL) soils are unpublished data of M.C. 
Reheis; values for Kyle Canyon soils are from Reheis and others (1992); and values for Wilson 
Creek (WC) soils are unpublished data of J.W. Harden.

file dsolmin.xls
The clay mineralogy of soils from published sources was compared to that of modern dust 
at the same sites (see datafile "dustmin.xls").  Observed differences between the clay mineralogy of 
soils and dust at some sites are attributed either to clay formation within the soils, to variability not 
explored sufficiently because too few samples were analyzed, or to slightly different analytical 
procedures used for the soil and dust samples (different ion saturations, etc.).  In addition, the 
published reports used different methods to estimate abundances of clay minerals from peak 
heights on X-ray diffraction traces.  Soils at Silver Lake were analyzed, and relative abundances of 
clay minerals estimated, using the same techniques used for the dust samples.
Values for Whipple Mountains soils are from McFadden (1982); values for Silver Lake 
soils are unpublished data of M.C. Reheis; values for Fortymile Wash soils are from Taylor 
(1986);  values for the Mormon Mesa calcrete are from Gardner (1972); values for the Cima 
volcanic field soils are from McFadden et al., 1986); and values for the Kyle Canyon soils are 
from Amundson et al. (1989).

file averate.xls
Accumulation rates were calculated for pedogenic silt, clay, CaCO3, and salt depending on 
the availability of data.  At sites with more than one analyzed soil profile of the same age, the 
profile-weight values were averaged.  The average "best" accumulation rates were calculated using 
the "best" age (the most reasonable age assigned to the geomorphic surface), and average 
maximum and minimum rates were calculated using the likely minimum and maximum ages 
respectively.  The following are example calculations for the silt accumulation rate of soils on 
surface Q5, Coyote Mountains, where the average profile weight of silt in Q5 soils is 0.8 g/cm2, 
the "best" age is 12 ka, the minimum age is 9 ka, and the maximum age is 20 ka:
average "best" accumulation rate = 0.8 g/cm2 / 12,000 yr = 0.7 g/m2/yr
average maximum accum. rate    = 0.8 g/cm2 /   9,000 yr = 0.9 g/m2/yr
average minimum accum. rate     = 0.8 g/cm2 / 20,000 yr = 0.4 g/m2/yr

file intrate.xls
  The interval-accumulation rate for each profile is the rate of accumulation of a pedogenic 
component in a soil forming on a surface from the time of deposition of that surface to the time of 
deposition of the next younger surface.  If there is no younger profile, the interval rate is the same 
as the average rate.  Interval age is the period of time between the formation of one surface and the 
formation of the next younger surface.
	Best interval age = best age (older) - best age (younger).
	Minimum interval age = minimum age (older) - maximum age (younger).
	Maximum interval age = maximum age (older) - minimum age (younger).
As an example, the "best" interval accumulation rate between soils formed on surfaces Q5 
and Q4 of the Coyote Mountains, where the average profile weight of silt in Q4 soils is 0.4 g/cm2 
and the "best" age is 3 ka is calculated by:
interval accum. rate = (0.8 g/cm2 -  0.4 g/cm2) / (12,000 - 3,000 yr) = 0.4 g/m2/yr
The interval-rate value is plotted at the midpoint between the two "best" ages, or at 7,500 years.
Soil accumulation rates must be treated with caution.  (1) Variation in amount of a 
pedogenic material is expectable for soils of the same age because soils are inherently variable.  
Data from more than one profile per geomorphic surface is critical for quantitative soil studies (e.g. 
data for field properties of soils at Silver Lake; Reheis and others, 1989).  Standard deviations 
were only calculated for the interval rates at the Fortymile Wash area, Silver Lake, the Cima fans, 
Wilson Creek, and the Coyote Mountains, which had quantitative data for more than one profile 
per surface (file "intrtdev.xls").  Excluding soils that were strongly eroded or leached, the standard 
deviations average 75% of the rates, but range widely (5-200%).  (2) There are uncertainties in the 
assigned ages of the geomorphic surfaces and their soils.  This problem is most acute for the 
youngest deposits; for example, if a deposit is thought to be 200 years old but in fact is 400 years 
old, an error of only 200 years would yield a doubled accumulation rate.  In addition, radiometric 
ages are available only for soils from Silver Lake, the Fortymile Wash area, Kyle Canyon, and the 
Coyote Mountains.  We have not included age uncertainties in the calculation of interval rates 
because generally the minimum and maximum ages greatly exaggerate the probable errors.  For 
studies in which the ages of soils were better constrained, as at Silver Lake and Fortymile Wash, 
interval-rate uncertainties calculated from the minimum and maximum soil ages were similar to the 
range of standard deviations calculated using replicate soils of the same age.  (3) Assumptions and 
simplifications were used in the calculations of profile weights of pedogenic materials, mainly in 
the estimation of parent-material values and of bulk density (in this study, a range of 1.2-2.0 
g/cm3), which is difficult to measure accurately in gravelly deposits (Vincent and Chadwick, 
1994).

file intrtdev.xls
Averages and standard deviations were computed for the "best" interval-accumulation rates 
for sites that had data for more than one soil profile of the same age.  Calculations followed the 
same procedures described in file "intrate.xls" except that to obtain the interval mass, the average 
interval mass of a younger group of soils was subtracted from the individual interval mass of the 
next older soil or soils. 

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349-371.
Baedecker, P.A., 1987, ed., Methods for Geochemical Analysis: U.S. Geological Survey Bulletin 
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Birkeland, P.W., 1984, Soils and Geomorphology: New York, Oxford University Press, 372 p.
Gardner, L.R., 1972, Origin of the Mormon Mesa caliche, Clark County, Nevada: Geological 
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Gile, L.H., Peterson, F.F., and Grossman, R.B., 1966, Morphological and genetic sequences of 
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Goodmacher, J., and Rockwell, T., 1990, Properties and inferred ages of soils developed in 
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