Playa lakes, pluvial lake basins, playa wetlands.
nia, Arizona, and Nevada, as well as of the Sahara, Lib-
On the southern High Plains of Texas and New
yan, and Arabian Deserts (Stone 1956). Playas are a dis-
Mexico (and also extending throughout the South-
tinct part of the landscape; although their surfaces often
ern Great Plains to include Colorado, Kansas, and
represent Pleistocene lakebeds, portions of the relict
Oklahoma), there are some 30,000 small (<1.6 km
lakebed surface may be covered by dunes (composed,
[1 mi] diameter), ephemeral lakes, with geological
at least in part, of alluvial material deposited by streams
origins in ephemeral or relict stream channels
feeding the former lake) and alluvial slopes (Motts 1970)
(Nelson et al. 1983, Cooke et al. 1993, Gustavson
(Fig. 1). The geomorphology of playas may be quite
et al. 1994; see also review by Reeves 1966). These
complex. For example, in the Mojave Desert, where three
are generally small, internally drained circular
playas are situated on what was Pleistocene Lake
depressions that collect runoff and focus recharge
Thompson, two (Rosamond and Rogers playas) are
to the Ogallala aquifer. They are typically flooded
thought to be at the level of the original lakebed, but a
13 months each year and the flooding may elimi-
third (Buckhorn) is somewhat higher in elevation. The
nate vegetation from the lower portions (Gustavson
latter may have a different genesis.* Frequently, small
et al. 1994). Briere (2000) denotes them as being tran-
playas may occur near the margins of larger playas in
sitional between a playa and a lake; neither dry more
depressions defined by dunes, or behind relict beach
than 75% of the time nor wet more than 75% of the
ridges on the edges of playas (Stone 1956). An example
time. There may also be a gradient in both plant
of such a formation exists in the vicinity of Troy Dry
Lake, California, where 2030 small playas developed
ing depth and period of inundation (Gustavson et
in the very slight depressions in the alluvial material
al. 1994). These playas, when flooded, range from
bordering the main playa (Stone 1956). Similar such pla-
nonsaline, when flood water is lost via deep perco-
yas exist at Cuddeback, Rogers, Rosamond, and Buck-
lation to a water table, to saline, when water is lost
horn Dry Lakes, California. Small playas may also occur
in irregularities in alluvial fans that are far removed from
Pans. The term pan (panne) is used in a range of
larger playas, in enclosed basins formed by faulting, or
ways. In Southern Africa, Australia, and occasion-
other depressions formed by similar processes (Stone
ally in the United States, it (or salt pan or lime pan)
1956). The edges of most barren playas are character-
is synonymous with playa (Johnson and Oliver
ized by an increase in vegetation, sediment size, and
1997); in the United States pan or clay pan may
slope. Geologically, these edges may represent relict
refer to small playa or playa-like areas that are gen-
wave-formed bars, beach ridges, or alluvial deposits.
erally unvegetated (Shaw and Thomas 1989). Clay
These changes, while generally abrupt, may be some-
pan may also refer to a variety of other similar but
times very gradual without clear boundaries (Neal 1965).
not geologically related features such as vernal
Although playas are defined in part as internally
pools. Salt pan is also used to denote small, non-
drained, the playa boundaries as geologically defined
vegetated depressions in coastal salt marshes.
may not correspond to boundaries that currently are or
Sabkha. Sabkhas are coastal saline flats in North
could become inundated. Further, the historic bound-
Africa closely resembling playas in appearance
aries of inundation may not correspond to current pat-
and characteristics. They are hard, salt-encrusted,
terns.
flat surfaces lying above the high tide line but occa-
sionally becoming inundated with seawater dur-
PLAYA HYDROLOGY
ing storm conditions (e.g., Akili and Torrance 1981,
Briere 2000). Sometimes, playas are inappropriately
Few technical data are available documenting the
(Briere 2000) referred to as continental sabkhas.
areal extent of inundation of playas; playa hydrology
Dayas (North Africa), Balte (Libya), Dongas
has been reviewed recently (Rosen 1994) with the con-
(Australia), Vleis (southern Africa), Chor or Sor
clusion that relatively little is known. Water may accu-
(Central Asia). These are small depressions on
mulate on playas from surface runoff, direct precipita-
flat expanses of limestone or calcrete areas that
tion, or groundwater discharge. Annual variation is such
may intermittently flood (Cooke et al. 1993) and
that a particular playa may not become flooded at all
thus bear some resemblance to playas.
during a particular year or remain flooded for up to three
years (Cooke et al. 1993). This is due in part to the na-
LANDSCAPE SETTING OF PLAYAS
Playas represent about 1.1 percent of the land sur-
* Personal communication, Dr. Anthony Orme, Professor of
face area of the Mojave and Sonoran deserts in Califor-
Geology, UCLA, Los Angeles, California, 1995.
4
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