36
WALLACE H. FULLER
developed soil profiles are not uncommon on broad desert surfaces. Such
land surfaces appear to have been stabilized through glacial periods of
humid and interglacial periods of dry climate. Relic characteristics of ancient soils are more prominent in desert than the more humid areas. The
intensity of development of recent genetic horizons under humid conditions
tends to "obscure" or "reduce" relic characteristics. Argillic (clayey) horizons, some with deep layers of lime, found on certain desert floors and
buried in alluvial fans, also suggest that humid climates predominated at
one time.
B. ENTISOLS
Genesis of desert soils is complicated further by recent deposits of
alluvial debris from overflowing, raging streams during heavy rains in
adjacent mountains and foothills. Alluvial fans in the deserts of the Southwestern United States, for example, are still being covered, uncovered, and
dissected by arroyo floods from summer torrents. Soil patterns in desert
valleys are diverse due to the cutting and filing action of streams flowing
through the ages at different rates. Horizontal layerings of sand, silt and
clay of varying thicknesses are interspersed by lenses or islands, also of
different textures (see Fig. 3). Sparse vegetation invites shifting sand and
Fig. 3. Alluvial soil showing typical stratification of different textures of sand,
»ilt, and clay.
WALLACE H. FULLER
developed soil profiles are not uncommon on broad desert surfaces. Such
land surfaces appear to have been stabilized through glacial periods of
humid and interglacial periods of dry climate. Relic characteristics of ancient soils are more prominent in desert than the more humid areas. The
intensity of development of recent genetic horizons under humid conditions
tends to "obscure" or "reduce" relic characteristics. Argillic (clayey) horizons, some with deep layers of lime, found on certain desert floors and
buried in alluvial fans, also suggest that humid climates predominated at
one time.
B. ENTISOLS
Genesis of desert soils is complicated further by recent deposits of
alluvial debris from overflowing, raging streams during heavy rains in
adjacent mountains and foothills. Alluvial fans in the deserts of the Southwestern United States, for example, are still being covered, uncovered, and
dissected by arroyo floods from summer torrents. Soil patterns in desert
valleys are diverse due to the cutting and filing action of streams flowing
through the ages at different rates. Horizontal layerings of sand, silt and
clay of varying thicknesses are interspersed by lenses or islands, also of
different textures (see Fig. 3). Sparse vegetation invites shifting sand and
Fig. 3. Alluvial soil showing typical stratification of different textures of sand,
»ilt, and clay.