tal morphology exhibits an abrupt change. Large-scale
regular seasonality in their surficial characteristics
polygons (1 m [3.28 ft] or more in diameter) may also be
(Langer and Kerr 1966). Interestingly, Motts (1972) sug-
present, with halite crystals actively growing around
gests that the cyclic crust formation and subsequent
the raised polygon edges. Such features are strong ev-
wind erosion is responsible for the slow lowering of the
idence that the playa experiences contemporary inun-
surface of playas such as Rogers and Rosamond.
dation on a regular, though undetermined, basis.
Some highly saline areas form pressure ridges of salt
VEGETATION
crust where freestanding salt crusts may form "blisters"
that rise above the ground surface to heights of 515
The relation between vegetation and OHW on pla-
cm (26 in.). These cracked and broken crusts have an
yas is tenuous and often confounded by many other
almost bubble-like, blistered appearance that may result
factors. Although the occurrence and abundance of
from a combination of surface inundation and subsur-
certain species of macrophytes is central to the meth-
face evaporation (Lines 1979). However, caution needs
odology for delineating wetlands, this is not the case
to be urged in interpreting hydrology from these blis-
for playas because of the usual (if not defining) absence
tered crusts, because they may form exclusively from
of vegetation, the spatially and temporally variable
subsurface transport via capillary and transpirative rise
hydrology, and the influences of extreme salinity and
aridity. Hydrophytic vegetation (sensu Tiner 1991) and
and subsequent precipitation. We have seen them near
the Salton Sea, California, on sides of berms and
the associated criteria for wetland delineation are
defined in the Corps of Engineers Wetlands Delinea-
phreatophytic mounds 50 cm (0.25 in.) above the eleva-
tion Manual (Environmental Laboratory 1987) and sub-
tion of possible flooding as well as on ground under-
lain by extensive networks of 4-ft- (1.22 m-) deep ground-
sequent guidance from the Office of the Chief of Engi-
water control tiles. Their surface extent is larger than
neers (1992, 1995). A national list of such species has
that of likely inundation, so they must result in some
been provided by the U.S. Fish and Wildlife Service
places largely from capillary rise of salt-saturated water.
(Reed 1988), the intent of which is to assist in locating
Hunt (1966) also describes such blistered crusts among
jurisdictional boundaries of wetlands. The "indicator
phreatophyte mounds in Death Valley, California.
status" of plants is a fundamental factor in delineating
wetlands. Because the ratings were developed for a
Soil structure and texture
wetland in the Cowardin classification and later adapted
The difference between soft and hard playas can be
for a three-parameter wetland, there are instances in
considered a difference in soil structure, which in turn
which the utility of the ratings breaks down and the
can be used to infer flooding regime because soft pla-
presence of these plants is problematic in establishing
yas form above a vadose zone and groundwater, where-
evidence for both OHW and wetland boundaries. On-
as hard playas form from inundation processes. The
ground experience has shown that the reliability of wet-
upper horizons of soft playas have strong, very fine
land plant species indicator statuses along playa edges
granular structure, are loose, very friable, have low bulk
are compromised by the occurrence of halophytes and
density, and often contain many fine, white, needle-
phreatophytes responding to highly saline soils and
shaped salt crystals. The surface horizons of hard pla-
groundwater at depths greater than included in the cri-
yas have massive to weak platy structure and are dense,
teria for wetland delineation. For example, Lichvar et al.
(1995) discuss problems with iodinebush (Allenrolfea
very hard, and nearly impermeable to water infiltration.
occidentalis), rated FACW (Facultative Wetland), on
Indeed, the soil a few inches below inundated hard pla-
yas may be dry (Stone 1956, Lichvar and Sprecher 1996).
soft playas. At Dugway Proving Ground, Utah, this
Playas usually have finer texture than the surround-
plant is a phreatophyte and occurs in areas that have
ing landscape, but textural differences themselves are
neither evidence of ponded water nor hydric soil. It is
not adequate to serve as "changes in the character of
assumed that its presence is related both to ground-
soil" for determining the OHW level (33 CFR
water within 1 m (3.28 ft) or more (which is otherwise
329.11[a][1]). Dunes on top of the playa, however, are
insufficient to produce a three-parameter wetland) and
likely to have coarser textures than the playa bed itself,
its ability to tolerate saline conditions.
allowing for exclusion from OHW delineations.
Playas, particularly hard playas, are commonly
All of the above patterns may change as a result of
devoid of macrophytes because of harsh physical con-
inundation; wind-induced water motion is a particularly
ditions (compact soil, high salinity, and unpredictable
effective force in smoothing surficial features from playa
cycles of inundated/dry conditions). There may be
surfaces. Even small amounts of water, such as that of
sparse growth on the playa edges and along drainage
a single rainstorm, may completely alter surficial pat-
channels, small depressions in the playa surface, cracks
terns (Neal and Motts 1967); some playas demonstrate
(e.g., desiccation cracks) that have filled in, phreato-
12
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