concentrations near the surface. The polygons are gen-
dence of ponding. Tracks left by boulders and other
erally five-sided, 1.8312.2 m (640 ft) in width, and
objects possibly blown across muddy surfaces have
bounded by ridges of salt from 0.3048 to 0.9144 m (1 to
been documented and are of particular interest at Race-
3 ft) high. They are common, but highly ephemeral
track Playa, Death Valley (see Bacon et al. 1996). Such
because they are obliterated during flooding. They are
impressions have been seen to be removed by wind ero-
common at Searles Lake and Death Valley Playa, Cali-
sion near Buckhorn Playa, California (Brostoff, unpub-
fornia.
lished).
Pressure-ridge salt crusts (Lines 1979) are initially
Other surface phenomena
flat, smooth crusts formed by evaporating surface
brines. As the crust dries and additional salt is deposited
"Sticky-wet surfaces" are continuously wet regard-
less of season and are composed of salt, silt, and clay
expands and forms sharp pressure ridges. The tops of
(Kerr and Langer 1965). They are typically associated
the ridges fracture with upturned edges as much as 5
with the salt pavement and soft crust types, e.g., Pilot
cm (0.19 in.) high. Diameter may be 0.30480.6096 m (1
Valley, Utah (Malek et al. 1990).
2 ft). These have been described for Bonneville Salt flats
"Gas pits, gas holes" are conical basins 0.300.9 m
in the United States and Chilean salars (Lines 1979) and
(13 ft) in diameter and from 15.24 to 91.44 cm (6 to 36
are also common at the Salton Sea, California (Sprecher,
in.) deep, with a smaller venthole (Stone 1956). The pits
personal observation).
are formed while the surface is underwater and are the
Carbonate surfaces may occur along the faulted
result of escaping gas (generally atmospheric in com-
playa border where springs deposit minerals that form
position). These are found in association with mud
a carbonate crust. This occurs in Death Valley (Kerr and
cracks. Representative gas pits are found at Coyote,
Langer 1965).
Buckhorn, and Lavic Dry Lakes, California.
Layered mudcracks 5.0810.16 cm (24 in.) deep with
subtended flat or smooth surfaces are common at the
SOILS, SURFACE, AND
lowermost areas that pond water during most inunda-
SUBSURFACE FEATURES
tion events (Lichvar and Sprecher 1996).
Soils
Erosion/surface impressions
Federal regulations recommend soil morphology as
"Rosette impressions" (Motts and Carpenter 1970)
a tool to help delineate the areal extent of wetlands and
are distinctive markings produced on flooded playas
OHW levels on playas. Specific rules have been devel-
by ice movement or ice crystal formation across mud
oped to distinguish hydric ("wetland") soils from upland
surfaces during alternate freezethaw cycles. In the pla-
soils (Environmental Laboratory 1987, U.S. Department
ya lakes of Canada, similar freezethaw cycles produce
of Agriculture, Natural Resources Conservation Service
a characteristic granularity in the soil (Renaut 1993).
1998). However, the only guidance given for using soil
"Desert flower" patterns are those characteristic den-
to identify OHW levels is "changes in the character of
dritic patterns 5.087.62 cm (23 in.) deep left by the
soil" (33 CFR 329.11[a][1]). This guidance does not iden-
erosive forces of water flowing into desiccation fissures
tify the nature of the changes or provide quantitative
(Motts and Carpenter 1970).
thresholds of color, depth, or abundance of soil features
on either side of the regulated playa boundary.
Drift lines, water marks
Because characteristics of both wetlands and pla-
Although not considered in the technical literature,
yas develop under conditions of periodic wetness, it is
discontinuities in the condition of litter, drift material,
tempting to apply hydric soil protocols to playa soils.
and the soil surface may also provide good evidence
Indeed, the U.S. Department of Agriculture, Natural
as to the extent of recent inundation. Drift lines (e.g.,
Resources Conservation Service (USDA NRCS) has
Fig. 3a, b, d) are specifically mentioned in the CWA as
proposed just such an indicator (Indicator TA1, Playa
an indicator of OHW. The presence of these markings
Rim Stratified Layers, USDA NRCS 1998) for sparsely
lends more credence to establish an OHW mark if they
vegetated playa rims. However, further applicability of
are continuous, thus indicating a spatially defined area.
hydric soil protocols to playas is limited by several char-
Other indicators also exist, but may appear similar
acteristics unique to playas.
on muddy but nonponded surfaces. Use of these indi-
First, hydrologic regimes for wetlands are more
cators requires caution and the capability to distinguish
strictly defined than for playas. In a particular intermit-
their occurrence on ponded vs. muddy areas. For exam-
tent lake bed, the OHW elevation may be higher than
ple, remnants of blown-in debris, animal tracks, boulder
that determined by the criteria for wetland hydrology
trails, and other objects have also been used as evi-
and needed to produce hydric soils. Second, hydric soil
9
to contents