[Illustration: SIERRA SERI FROM ENCINAS DESERT]
2. Sierra Seri is a double range, divided mid-length by a broad saddle
barely 2,000 feet in height.[13] Like other Sonoran ranges, the nucleal
portions are exceedingly rugged and precipitous—at least two of its
picachos shoot so boldly that they commonly seem to overhang, and have
been called leaning peaks. In large part the precipices rise abruptly
from a symmetrical dome molded by sheetflooding, much as the insulated
buttes rise from the Bacuache fan in northeastern Seriland; so that the
tract lying between Desierto Encinas and El Infiernillo is a composite
of exceptionally precipitous and exceptionally smooth mountain slopes.
One of the Seri trails radiating from Barranca Salina lies across the
mid-sierra saddle; others push into several mountain valleys, and the
largest leads to Tinaja Trinchera, at the base of Johnson peak, where
there are a few low walls of loose-laid rubble, somewhat like those
of the trincheras (entrenched mountains) farther eastward—the only
structures of the sort seen in Seriland. Toward the southern end of
the range lie various trails, the most conspicuous paralleling the
coast, either near the shore or over the steep salients, according
to the configuration; while here and there ruinous jacales a few
yards from the coast attest sporadic habitation. The eastern shore of
Bahia Kunkaak from Punta Ygnacio northward reveals a typical geologic
section of the Sonoran province: the transgressing waves have carved
in the granitic subterrane a broad shelf lying just below mean low
tide and usually stretching several furlongs offshore; this shelf
is relieved here and there by remnantal crags of obdurate rocks,
cumbered by bowlders and locally sheeted with sand and arkose derived
from mechanically disintegrated granite; while the inner margin of
the shelf is a sea-cliff, usually 30 to 50 feet high, of which the
lower half is commonly granite and the upper half unconsolidated and
recent-looking mechanical debris collected by sheetflood erosion.
Sometimes the granite of the subterrane is replaced by volcanics;
sometimes ancient and firmly cemented talus deposits separate the
superficial mantle from the subterrane, as shown in the lower part
of plate V; sometimes the line of sheetflood planation passes below
tide-level, when the waves beat against the unconsolidated deposits in
a deep embayment; sometimes the sharply defined planation surface ends
abruptly at the sides of subranges or buttes shooting upward in the
abrupt slopes characteristic of the sierra proper; yet this 10-mile
stretch of coast is a nearly continuous revelation of the structure of
sheetflood-carved plains and of modern marine transgression. The debris
of the combined processes forms an abundant and varied assortment of
bowlders, cobbles, and pebbles, whence the inhabitants readily derive
their simple implements without need for studied forethought or manual
cunning.
[13] The northern portion, as seen from the east, is shown in plate
III; the southern portion, as seen from the west, appears in the upper
part of plate IV, while the southwesternmost point is shown in the
lower part of the same plate.
The long sand-spit terminating in Punta Miguel and the shorter one
terminating in Punta Arena are the product of geologically recent
wave building, and consist of irregular series of V-bars, backed by
lagoon-like basins and enclosing considerable bodies of brine in
the central portions; and the bars and basins become successively
higher outward, in such wise as to attest the secular subsidence of
this coast. Several jacales are located on the higher portion of the
southern sand-spit, midway between Punta Granita and Punta Miguel,
while footpaths traverse the flat and skirt the coast. Toward the
terminal portion of the spit the sand is blown into hummocks, held
by clumps of salt-enduring and sand-proof shrubbery; but there are
no rancherias here, despite the fact that it is a natural point of
embarkation—doubtless because no Seri structure could withstand the
sand-drifting gales and storm inundations of this exposed spot.
The more protected lagoons behind the outer bars harbor abundant
waterfowl, within bowshot of shrub-clumps and dunes well adapted to
the concealment of hunters, while the mud-flats open to the tide
abound in clams and other edible things. The features of the Punta
Miguel sand-spit are repeated with variations along the eastern shore
of El Infiernillo; and Seri jacales, evidently designed for temporary
occupancy, occur here and there, usually on higher banks above reach of
the severer storms.
3. Tiburon island itself is apparently the chosen home of the
Seri—a habitat to which the mainland tract is at once a dependency,
an alternative refuge, and a circumvallation. Its dominant range,
Sierra Kunkaak, mates Sierra Seri in its essential features, though
the rocks are for the greater part ordinarily obdurate eruptives
rather than exceptionally obdurate granites, as in the mainland
sierra; accordingly the range is somewhat lower and broader, while
the sheetflood sculpture, with its sharp transition into precipitous
cliffs, is somewhat less trenchant. Sierra Menor is a third term in
the mountain series, in structure and geomorphy as in altitude; while
the interior plain is a homologue of that portion of Desierto Encinas
lying north of Playa Noriega—i. e., of its (potentially) free-drained
portion. Almost the entire perimeter of Tiburon is suffering marine
transgression, and is faced with seacliffs overlooking wave-carved
shelves; and in both form and structure the greater part of the coast
repeats, with minor variations, the features of the mainland coast
from Punta Ygnacio northward. Partly because of the superior magnitude
and height of its debris-yielding sierra, partly because of protection
from the wave-beat of the open gulf, the eastern shore is skirted
with a talus-shape slope, usually two to four miles wide; and while
there are unmistakable evidences of sheetflood carving in the higher
portions of this plane, the coastal cliff commonly reveals nothing
but heterogeneous debris, sometimes rising thirty or forty feet above
tide. Somewhat the greater part of the volume of this debris is fine—i.
e., sand and silt and nondescript rock-matter; but there is always a
considerable element of larger rock-fragments, which gather along the
shore in a pavement of bowlders and cobbles (upper figure of plate V).
These coarse materials—important factors in aboriginal industry—are
harmoniously distributed; more conspicuously on the ground than on
the map, the coast is set with salients (of which Punta Narragansett
is a type), consisting merely of exceptional accumulations of debris
from gorges in the sierra and from shallow arroyos, or pebble washes,
traversing the coastwise plain. These salients owe their prominence
partly to the relative coarseness, partly to the abundant supply, of
fragmental material from the heights; and about their extremities the
beach is paved with bowlders, which grade to cobbles or even to pebbles
along the reentrant shores on either hand. This distribution of cobbles
is one of the conditions governing the placement of Seri rancherias;
and in many cases the jacales are located, either singly or in groups,
where the coastal salients and reentrants meet, and where there is an
abundant supply of cobbles of convenient size and wave-tested hardness.
[Illustration: BUREAU OF AMERICAN ETHNOLOGY