II. DESERT SOILS
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The subgroups have a cambic, calcic, petrocalcic, gypsic, or salic horizon,
or duripan characteristics.
1. Calciorthids
Calciorthids have either a calcic or gypsic horizon that has its upper
boundary within 1 meter of the surface. They have no duripan or petrocalcic horizon that has its upper boundary within 1 meter of the surface
and no salic horizon above the calcic or gypsic horizon, although these
soils are calcareous above the calcic or gypsic layer. Calciorthids are found
commonly in North American deserts in various stages of formation. In
early stages the lime is dispersed in the soil as a soft powder or appears
as coatings or pendents on the lower sides of gravel and stones. As time
progressed lime accumulated in and throughout the soil in pores until the
calcic layer became packed with lime and cemented. In certain soils lime
continued to be carried downward but because of inhibition of free movement of the water, it accumulated until it formed a continuous, smooth
layer. This indurated lime layer then became a petrocalcic horizon and
the soil is called petrocalcic Calciorthid. Certain of the Calciorthids may
have very little if any lime in the upper few centimeters but a definite
accumulation of lime at lower depths. Very sandy soils may be free of
lime as deep as 10-12 cm but pass abruptly into heavy concentrations of
lime. Gypsum often occurs with lime accumulations in desert soils of the
Southwestern United States and Mexico in variable amounts. In general,
however, the carbonates greatly exceed the sulfates. The calcium that accumulates is believed to come from relic deposits, parent material and/or
transient dust, as explained earlier. Parent material in situ alone does not
explain the large lime deposits often observed in calcic or gypsic soils.
2. Camborthids
Camborthids are Aridisols that have a changed or altered horizon (cambic horizon) or are young Aridisols that have received little carbonates.
They have no duripan, salic, calcic, gypsic, or petrocalcic horizon that has
its upper boundary within 1 meter of the surface. More recent soil-forming
processes have altered the material such that structure may be observed
if textures are suitable. Silica clays form with the loss of free iron oxides.
The peds lack distinct coatings and, like argillic layers, have randomly oriented particles and little pore space in the matrix.
3. Durorthids
Durorthids are Orthids that have a duripan whose upper boundary is
within 1 meter of the surface and are with or without a cambic horizon.
They have no petrocalcic horizon whose upper boundary is within 1 meter
41
The subgroups have a cambic, calcic, petrocalcic, gypsic, or salic horizon,
or duripan characteristics.
1. Calciorthids
Calciorthids have either a calcic or gypsic horizon that has its upper
boundary within 1 meter of the surface. They have no duripan or petrocalcic horizon that has its upper boundary within 1 meter of the surface
and no salic horizon above the calcic or gypsic horizon, although these
soils are calcareous above the calcic or gypsic layer. Calciorthids are found
commonly in North American deserts in various stages of formation. In
early stages the lime is dispersed in the soil as a soft powder or appears
as coatings or pendents on the lower sides of gravel and stones. As time
progressed lime accumulated in and throughout the soil in pores until the
calcic layer became packed with lime and cemented. In certain soils lime
continued to be carried downward but because of inhibition of free movement of the water, it accumulated until it formed a continuous, smooth
layer. This indurated lime layer then became a petrocalcic horizon and
the soil is called petrocalcic Calciorthid. Certain of the Calciorthids may
have very little if any lime in the upper few centimeters but a definite
accumulation of lime at lower depths. Very sandy soils may be free of
lime as deep as 10-12 cm but pass abruptly into heavy concentrations of
lime. Gypsum often occurs with lime accumulations in desert soils of the
Southwestern United States and Mexico in variable amounts. In general,
however, the carbonates greatly exceed the sulfates. The calcium that accumulates is believed to come from relic deposits, parent material and/or
transient dust, as explained earlier. Parent material in situ alone does not
explain the large lime deposits often observed in calcic or gypsic soils.
2. Camborthids
Camborthids are Aridisols that have a changed or altered horizon (cambic horizon) or are young Aridisols that have received little carbonates.
They have no duripan, salic, calcic, gypsic, or petrocalcic horizon that has
its upper boundary within 1 meter of the surface. More recent soil-forming
processes have altered the material such that structure may be observed
if textures are suitable. Silica clays form with the loss of free iron oxides.
The peds lack distinct coatings and, like argillic layers, have randomly oriented particles and little pore space in the matrix.
3. Durorthids
Durorthids are Orthids that have a duripan whose upper boundary is
within 1 meter of the surface and are with or without a cambic horizon.
They have no petrocalcic horizon whose upper boundary is within 1 meter