go to: Contents : Next Article
The Edwards Plateau has been dissected by stream erosion to yield a rugged
topography referred to locally as the "Hill Country." Its main physiographic
component is gently sloping interstream uplands. These relatively level
uplands are interrupted by steep slopes and canyon walls of stream courses.
The Edwards Plateau is a limestone terrane rife with fissures that carry water
to springs that in turn keep the streams supplied.
The limestones of the upland divides are slowly carried off in solution by
carbonic acid-laced water. The only particulate matter available to form a
soil residuum is the minor percent of clay and sand admixed within the
limestone. But the steepness of the slopes allows a rapid runoff of rain that
commonly results in erosion of clastic material before a mature soil profile
can develop. Thus, the area is characterized by thin soils mixed with broken
rock slabs that rest on hard limestone.
The region annually receives from 15 to 30 inches of rain, but its distribution
in time and space is highly irregular. Several years may see far less than the
mean annual rainfall, but then the precipitation during one week may exceed the
yearly average. Mean annual temperature is in the high 60's, but winter
readings drop below freezing for short periods and summer values sometimes
exceed 100 degrees. Winds dominantly come from the southeast from the Gulf of
Mexico and evaporation rates are considerably in excess of precipitation.
The eastern Edwards Plateau is covered by open grassland and scattered scrub
timber. The timber of the divides is a dry-climate forest picturesquely
described by Bray in a 1904 USDA Forestry Bulletin:
"The growth is stunted, the wood dense and hard, the branches rigid, the
foliage somber, the leaves small and stiff; the climate is written in every
feature."
The native vegetation is largely short grasses, bunch grasses, abundant
junipers, various oaks, mesquite, cacti, and many shrubs. It is used
predominantly as range land and is commonly stocked with combinations of
cattle, sheep and goats to make the best economic use of the variety of plants.
The steep limestone slopes and gentler uplands are dominated by a
juniper-oak-grass floral association. The most abundant tree is Juniperus
ashei. This juniper (known as cedar to "Hill Country" folk) flourishes in
the harsh calcareous soils of central Texas and on similar limestone terranes
in southern Oklahoma and southeastern Missouri.
Oaks common to the area have geographic distributions over large parts of the
Atlantic and Gulf coastal plains (Fowells, 1965). These oaks include
Quercus sinuata (white or shin oak), Q. virginiana (live oak),
and Q. shumardii (Texas or Spanish oak). The westernmost
extent of each oak
species an a range map is separated by a dashed line essentially delimiting the
Balcones fault trace. West of this line these wide-ranging oak species have
had to undergo ecotypic differentiation in order to adjust to the thin,
seasonally dry, calcareous soils of the Edwards Plateau. Thus they are further
described by the respective varieties: breviloba, fusiformis, and
texana. The harsh soils derived from the limestone terrane and the
spasmodic rainfall have caused habitat-correlated variation within each species
which has created genetically fixed ecotypes. These varieties are found also in
southwest Oklahoma and on the east face of the Sierra Madre Oriental in
Mexico.
The distinctive, stunted vegetation on the Edwards Plateau forms an extensive
tract of wasteland known in other regions as a heath. This broad area of
rather level, open, uncultivated land with poor soil and a dominant floral
element creates an ambiance that affects some people to the essence of their
being. In psychological effect the Edwards Plateau and its vegetation create a
mood not unlike that of the great heaths of southern England so memorably
described by Thomas Hardy in the Return of the Native (1878). The following
excerpt has been modified slightly from Hardy's original words:
"The face of the heath by its mere complexion added half an hour to evening; it
could in like manner retard the dawn, sadden noon, anticipate the frowning of
storms scarcely generated, and intensify the opacity of a moonless midnight to
a cause of shaking and dread.
In fact, precisely at this transitional point of its nightly roll into darkness
the great and particular glory of the Edwards waste began, and nobody could be
said to understand the heath who had not been there at such a time. It could
best be felt when it could not clearly be seen, its complete effect and
explanation lying in this and the succeeding hours before the next dawn; then,
and only then, did it tell its true tale. The sombre stretch of rounds and
hollows seemed to rise and meet the evening gloom in pure sympathy, the heath
exhaling darkness as rapidly as the heavens precipitated it. And so the
obscurity in the air and the obscurity in the land closed together in a black
fraternization towards which each advanced halfway.
The place became full of a watchful intentness now, for when other things sank
brooding to sleep the heath appeared slowly to awake and listen. Every night
its Titanic form seemed to await something; but it had waited thus, removed,
during so many centuries, through the crises of so many things, that it could only be imagined to await one last crisis--the final overthrow.
It was a spot which returned upon the memory of those who loved it with an
aspect of peculiar and kindly congruity. Smiling champaigns of flowers and
fruit hardly do this, for they are permanently harmonious. Twilight combined
with the scenery of Edwards Heath to evolve a thing majestic without severity,
impressive without showiness, emphatic in its admonitions, grand in its
simplicity. The qualifications which frequently invest the facade of a prison
with far more dignity than is found in the facade of a palace double its size
lent to this heath a sublimity in which spots renowned for beauty of the
accepted kind are utterly wanting. Men have oftener suffered from the mockery
of a place too smiling for their reason than from the oppression of
surroundings oversadly tinged. Haggard Edwards appealed to a subtler and
scarcer instinct, to a more recently learnt emotion, than that which responds
to the sort of beauty called charming and fair.
The most thorough-going ascetic could feel that he had a natural right to
wander on Edwards: he was keeping within the line of legitimate indulgence when
he laid himself open to influences such as these. Colours and beauties so far
subdued were, at least, the birthright of all. Intensity was more usually
reached by way of the solem than by way of the brilliant, and such a sort of
intensity was often arrived at during winter darkness, tempests, and mists.
Then Edwards was aroused to reciprocity; for the storm was its lover, and the
wind its friend. Then it became the home of strange phantoms; and it was found
to be the hitherto unrecognized original of those wild regions of obscurity
which are vaguely felt to be compassing us about in midnight dreams of flight
and disaster, and are never thought of after the dream till revived by scenes
like this.
It was at present a place perfectly accordant with man's nature--neither
ghastly, hateful, nor ugly: neither commonplace, unmeaning, nor tame; but, like
man, slighted and enduring; and withal singularly colossal and mysterious in
its swarthy monotony. As with some persons who have long lived apart, solitude
seemed to look out of its countenance. It had a lonely face, suggesting
tragical possibilities.
The untameable, Ishmaelitish thing that Edwards now was it always had been.
Civilization was its enemy; and ever since its beginning its soil had worn the
same antique brown dress, the natural and invariable garment of the particular
formation. In its venerable one coat lay a certain vein of satire on human
vanity in clothes. A person on a heath in raiment of modern cut and colours
has more or less an anomalous look. We seem to want the oldest and simplest
human clothing where the clothing of the earth is so primitive.
To recline on a stump between afternoon and night, where the eye could reach
nothing of the world outside the summits and shoulders of heathland which
filled the whole circumference of its glance, and to know that everything
around and underneath had been from prehistoric times as unaltered as the stars
overhead, gave ballast to the mind adrift on change, and harassed by
irrepressible New. The great inviolate place had an ancient permanence which
the sea cannot claim. Who can say of a particular sea that it is old?
Distilled by the sun, kneaded by the moon, it is renewed in a year, in a day,
or in an hour. The sea changed, the fields changed, the rivers, the villages
and the people changed, yet Edwards remained. Those surfaces were neither so
steep as to be destructible by weather, nor so flat as to be the victims of
floods and deposits."
in Abbot, Patrick L. and Woodruff, C.M., Jr., eds., 1986,
The
Balcones Escarpment, Central Texas;
Geological Society of America, p.33-34
go to: Contents : Next Article
