4 INSTITUTE OF SOCIAL ANTHROPOLOGY—PUBLICATION NO. 7 
shallow southern part of the lake lie JarAcuaro, 
the largest of the group, and the newly formed 
Pastora. (The former island of Copujo is now 
attached to the mainland.) Both islands are low, 
composed of semiconsolidated alluvial materials. 
Along the southern shore only low marsh now 
separates the Urandén islets (low voleanic hills) 
from the mainland (pl. 1). 
The southern escarpment.—Although geologi- 
cally similar to the Sierra, the abrupt southern 
escarpment, which forms part of the Mesa 
Central’s southern wall, constitutes a distinct 
physiographic area. Pleistocene and Recent 
vulcanism continues from the Sierra to the Balsas 
and Tepalcatepec Rivers, Jorullo having been the 
most recent volcanic activity on the escarpment. 
The canyons formed by deeply entrenched spring- 
fed streams are the escarpment’s salient features. 
Some barrancas exceed 500 feet in depth. The 
upper tributaries of the escarpment streams are 
eroding headwardly into the Sierra, capturing 
enclosed basins and intermittent water courses.’ 
Above the barranca area shallow basins occur in 
the upper portion of the escarpment. Probably 
of volcanic origin, these flattish-floored valleys are 
now tapped by escarpment streams. Typical 
examples are the plains surrounding Uruapan, 
those below Periban and Los Reyes, the valleys 
of Tingambato and Tacambaro, all important 
sites of former Tarascan settlement in the tierra 
templada. 
The northern plateau area.—The former Taras- 
can area north of the Sierra forms part of the 
interior plateau county of Central Mexico. For 
the most part physiography is characterized by 
old volcanic hills and mountains separated by 
flat to rolling plains country. The part of this 
region formerly inhabited by Tarascans extends 
from Lake Chapala east to the Sierra de Ozumatlan 
and from the Sierra north to the Lerma River. 
(The low areas near the river and its tributaries 
are often termed the ‘Bajio.”’) A narrow belt 
of the hill and plains landscape also extends south 
from Lake Chapala to include the Cotija-Tin- 
giiindin area along the western side of the Sierra. 
Average elevations in the interior plateau decrease 
from 7,200 feet along the flanks of the Sierra de 
Ozumatlin to 5,000 feet at Lake Chapala. The 
7 For example, this phenomenon has occurred at the southwestern edge 
of the Sierra, where a tributary of the Tepaleatepee has apparently captured 
the drainage of the structural basin which runs east-west from Parangaricu- 
tiro to Periban. 
higher hills and mountains rise 2,600 to 4,000 
feet above the surrounding plains. 
The young volcanic land forms found in the 
Sierra are lacking in much of the northern area, 
where the principal elevations consist of eroded 
composite Tertiary voleanoes. A few tongues of 
Recent lava flow from the Sierra into the northern 
edge of the plains, and cinder cones extend north- 
ward from El Zirate. Many lakes, some cecupy- 
ing structural basins, dot the northern area. The 
extensive sections of old alluvium, which form a 
good part of the plains, probably represent beds 
of Pleistocene lakes. At the northern and north- 
western base of the Sierra many spriag-fed lakes 
and marshes existed in historical times, e. g., 
Ciénaga de Zacapu, de Tangancicuaro, de Chapala, 
ete. The lacustrine basins and the borders of 
the former lakes and marshes were the major 
areas of Spanish settlement in the Tarascan North, 
for both afforded year-round pasture and _ sites 
for irrigated wheat farms. Some marshy sections 
still exist, but natural desiccation and artifical 
drainage have converted much of the wet area 
to dry farmland. The once extensive chain of 
lakes in the Cotija graben, west of the Sierra, has 
almost completely disappeared, and the marshes 
of Zacapu, around which are grouped a few rem- 
nant Tarascan pueblos, have been converted into 
a large farming area. 
A unique physiographic subarea of the northern 
zone, called “La Canada,” a narrow east-west 
depression at the northern base of the Sierra, is 
still one of the significant Tarascan regions. The 
valley floor, 10 km. long and 2 km. wide, decreases 
rapidly in altitude from 6,360 feet at its eastern 
end to 5,840 feet at Chilchota, near the western 
extremity (pl. 1). The western end of the valley 
is marked by an ancient lava flow, which once 
partially blocked normal drainage. Subsequent 
deposition of alluvium (possibly lacustrine) behind 
the lava dam has resulted in the present wide 
flattish floor of the valley’s western half. Today 
the stream draining the valley flows subsequently 
through a deep gorge cut through the northern 
end of the lava flow. The numerous intermittent 
streams which descend from the adjacent hills 
have built up small alluvial fans along the valley 
sides. Like other areas at the edge of the Sierra, 
La Canada is favored by numerous large springs 
issuing from fissures at the southern and eastern 
borders of the depression. Alluvium and water 
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