Seriland forms part of a great natural province lying west of the
Sierra Madre of western Mexico and south of an indefinite boundary
about the latitude of Gila river, which may be designated the Sonoran
province; it differs from Powell’s province of the Basin ranges in that
it opens toward the sea, and also in other respects; and it is allied
in many of its characteristics to the arid piedmont zone lying west of
the Andes in South America.
In general configuration the province may be likened to a great
roof-slope stretching southwestward from a comb in the Sierra Madre
to a broad eaves-trough forming Gulf of California, the slope rising
steeper toward the crest and lying flatter toward the coast; but the
expanse is warped by minor swells, guttered by waterways, and dormered
by outlying ranges and buttes. The most conspicuous inequality of the
slope (partly because of its coincidence with tide-level) is offered by
the rugged ranges of Seriland. These may be considered four in number,
all approximately parallel with each other and with the coast; the
first is a series of eroded remnants (Cerros Anacoretos) from 600 to
1,200 feet in height; the second is the exceedingly rugged Sierra Seri,
culminating in Johnson peak 5,000 feet above tide; the third is Sierra
Kunkaak, attaining about 4,000 feet in its highest point; the fourth is
Sierra Menor, some 2,000 feet high, with the northern extremity sliced
off obliquely by marine erosion. The principal arm of Desierto Encinas
lies between the first two ranges, El Infiernillo separates the second
and third, while a subdesert valley divides the third from the fourth.
The valleys correspond more closely than the ranges; if the land level
were 100 feet higher the strait and its terminal bays would become
an arid valley like the others, while if the sea-level were 500 feet
higher the four ranges would become separate islands similar to Angel
de la Guarda and others in the gulf.
The Sonoran province is notably warm and dry. The vapor-laden
air-currents from the Pacific drift across it and are first warmed by
conduction and radiation from the sun-scorched land, to be chilled
again as they roll up the steeper roof-slope to the crest; and the
precipitation flows part way down the slopes, both eastward and
westward from the Sierra Madre—literally the Mother (of waters)
range. A climatal characteristic of the province is two relatively
humid seasons, coinciding with the two principal inflections of the
annual temperature-curve, i. e., in January-February and July-August,
respectively. In the absence of meteorologic records the temperature
and precipitation maybe inferred from the observations at Yuma
and Tucson,[5] which are among the warmest and driest stations in
America, or indeed in the world; though it is probable that such
points as Caborca, Bacuachito, and Hermosillo are decidedly warmer
and perhaps slightly moister than Yuma. The ordinary midday summer
temperature at these points may be estimated at about 110° in the
shade (frequently rising 5° or 10° higher, but dropping 20° to 50°
in case of cloudiness); the night temperature at the same season is
usually 50° to 75°, though during two-thirds of the year it is liable
to fall to or below the freezing point. The sun temperature is high in
comparison with that measured in the shade, the exposed thermometer
frequently rising to 150° or 160°, according to its construction, while
black-finished metal becomes too hot to be handled, and dark sand and
rocks literally scorch unprotected feet. The leading characteristic of
the temperature is the wide diurnal range and the relatively narrow
annual range; another characteristic is the uniformity, or periodic
steadiness, of the maxima, coupled with variability and nonperiodicity
of the minima.
[5] The following monthly and annual meteorologic summaries, compiled
from United States Weather Bureau records at these stations, have
been kindly furnished by Prof. Willis L. Moore, Superintendent of the
Bureau. The tabulated records represent the observations of twenty
years at Yuma and ten years at Tucson.