VIM. PIMAN INDIANS OF THE SONORAN DESERT
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the whole region is generally between 13 and 25 cm; the intermontane valleys and mountain ranges are higher; and, unlike western Pimeria, parts
of the central area climb into the Upper Sonoran life zone. Its boundaries are the Sauceda-Batamote-Redondo-Ajo mountains on the west;
the Tucson-Sierrita-Cerro Colorado-Tumacacori-Atascosa-Pajarito mountains on the east; the Gila River on the north, excluding the river and flood
plain; and the Rio Magdalena and Rio Concepcion on the south, also excluding the rivers proper and their valleys (see Figs. 1 and 2).
a. Climate. Rainfall throughout the region, like that in the west, is biseasonal, but here most of it falls during the summer monsoons. At Gu Vo,
a Papago Indian village just east of the Ajo Mountains, the average annual
rainfall is 22.4 cm, with 12.6 cm falling in the summer and 9.75 cm in
the winter. At Sells, in the very heart of this more than 1,200,000 ha domain, the average annual rainfall is 25.2 cm, with 16.1 cm in summer and
9.16 cm during the comparatively more dry winter. At San Miguel, at the
southern end of the Baboquivari Valley in Arizona, the annual average
is 31.0 cm, two-thirds of it falling in summer and one-third in winter
(Bryan, 1925, p. 38; Hackenberg, 1964a, p. 65). The Baboquivari Mountains are topped by the 2360-meter Baboquivari Peak, and in the upper
reaches of such mountain ranges (including the Coyote and Quinlan
mountains) the rainfall figure is more than 38 cm/year. Throughout the
entire region the mean annual temperatures range from about 18° to 22°C
(Hastings and Turner, 1965, p. 185). Disregarding extremes related to
vertical heights of mountain ranges, the climate trends found in the Lower
Colorado Valley continue in the Arizona Upland: from east to west it becomes more warm, less wet, and less likely to rain more in summer than
in winter.
b. Physiography. The physiography is still characteristic of the Desert
Region of the Basin and Range Province, with its alternating mountain
ranges and valleys, both increasing in altitude above sea level moving from
west to east. Less that half the area is comprised of bajadas of low gradient or of intermontane plains, a marked contrast to the 85% of the Lower
Colorado Valley typified by such topography. Moving from west to east,
the major rows of mountains are the Sauceda-Batamote Redondo-Ajo
ranges, the Sand Tank-Mesquite mountains, Table Top-Vekol-Quijotoa
mountains, Tat Momoli-Santa Rosa-Comobabi-Artesa mountains, Silverbell-Roskruge-Coyote-Quinlan-Baboquivari mountains, and the eastern
boundary cited above. Major intervening valleys are the Rainbow-Vekol
and San Simon valleys, Santa Rosa-Gu Oidak-Tecolote valleys,
Baboquivari Valley, and the Altar (Avra) Valley (see Fig. 2).
Mountain slopes are less steep, pediments are wider, and the floors of
valleys are less flat and more sloping, with the drainages in their centers
505
the whole region is generally between 13 and 25 cm; the intermontane valleys and mountain ranges are higher; and, unlike western Pimeria, parts
of the central area climb into the Upper Sonoran life zone. Its boundaries are the Sauceda-Batamote-Redondo-Ajo mountains on the west;
the Tucson-Sierrita-Cerro Colorado-Tumacacori-Atascosa-Pajarito mountains on the east; the Gila River on the north, excluding the river and flood
plain; and the Rio Magdalena and Rio Concepcion on the south, also excluding the rivers proper and their valleys (see Figs. 1 and 2).
a. Climate. Rainfall throughout the region, like that in the west, is biseasonal, but here most of it falls during the summer monsoons. At Gu Vo,
a Papago Indian village just east of the Ajo Mountains, the average annual
rainfall is 22.4 cm, with 12.6 cm falling in the summer and 9.75 cm in
the winter. At Sells, in the very heart of this more than 1,200,000 ha domain, the average annual rainfall is 25.2 cm, with 16.1 cm in summer and
9.16 cm during the comparatively more dry winter. At San Miguel, at the
southern end of the Baboquivari Valley in Arizona, the annual average
is 31.0 cm, two-thirds of it falling in summer and one-third in winter
(Bryan, 1925, p. 38; Hackenberg, 1964a, p. 65). The Baboquivari Mountains are topped by the 2360-meter Baboquivari Peak, and in the upper
reaches of such mountain ranges (including the Coyote and Quinlan
mountains) the rainfall figure is more than 38 cm/year. Throughout the
entire region the mean annual temperatures range from about 18° to 22°C
(Hastings and Turner, 1965, p. 185). Disregarding extremes related to
vertical heights of mountain ranges, the climate trends found in the Lower
Colorado Valley continue in the Arizona Upland: from east to west it becomes more warm, less wet, and less likely to rain more in summer than
in winter.
b. Physiography. The physiography is still characteristic of the Desert
Region of the Basin and Range Province, with its alternating mountain
ranges and valleys, both increasing in altitude above sea level moving from
west to east. Less that half the area is comprised of bajadas of low gradient or of intermontane plains, a marked contrast to the 85% of the Lower
Colorado Valley typified by such topography. Moving from west to east,
the major rows of mountains are the Sauceda-Batamote Redondo-Ajo
ranges, the Sand Tank-Mesquite mountains, Table Top-Vekol-Quijotoa
mountains, Tat Momoli-Santa Rosa-Comobabi-Artesa mountains, Silverbell-Roskruge-Coyote-Quinlan-Baboquivari mountains, and the eastern
boundary cited above. Major intervening valleys are the Rainbow-Vekol
and San Simon valleys, Santa Rosa-Gu Oidak-Tecolote valleys,
Baboquivari Valley, and the Altar (Avra) Valley (see Fig. 2).
Mountain slopes are less steep, pediments are wider, and the floors of
valleys are less flat and more sloping, with the drainages in their centers