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- Panorama of Coporaque
(foreground) and Yanque (background-right), showing the Colca
river gorge in the center.
- The Colca Valley region lies on the western
slope of the western branch of the southern Peruvian cordillera,
in the Province of Caylloma, Department of Arequipa (see map). The region is dominated geographically
by great expanses of especially high, cold puna lands, punctuated
by volcanic peaks that reach altitudes of over 5000 and 6000
meters above sea level (masl). The 50 km-long central section
of the Colca River Valley was formed by fluvial incision into
this plateau during the Pleistocene. The valley is characterized
by a series of seven mesa-like alluvial benches of volcanic parent
material, divided by higher-angle slopes from the puna lands
above 4000 masl to the inner river gorge around 3300 masl (Sandor
1992). These bench surfaces, denominated Qal 1-7 (Quaternary
alluvium 1-7) increase in age with altitude, with the most recent
surface (Qal 1) at the modern entrenched river channel (Sandor
1992:233-234; Treacy 1989:65-67). Glaciated peaks lie above the
puna on both sides of the valley. The Nevados Mismi, Huillcaya,
and Quehuisha supply the glacial meltwater which constitute the
main source of water for the irrigation systems on the north
side of the Colca river. The Nevados Huarancate, Sabancaya, and
Ampato fulfill the same function for the south side of the valley.
Canal systems vary in length from a few kilometers to over thirty.
Most of the present valley population of 21,000 inhabitants is
distributed in twelve villages, originally constructed between
1571-1574 under the reducción policy of Viceroy Toledo
(Málaga 1977:116-123; Denevan et al. 1986:47).
- The project survey area is approximately 90 square kilometers in size, and surrounds the villages of Yanque and Coporaque (see
map). This specific area was chosen for a number of reasons.
First, the area chosen includes the kichwa and suni ecological
zones of the valley, as well as broad expanses of surrounding
puna where camelid pastoralism was likely to have been most intensive
(see Figure 2). Also, the greatest amount of archaeological research
has been conducted in this area of the valley, providing the
best possible preliminary information. Third, as observed in
the my preliminary reconnaissance (Wernke 1996, 1997), there
is a relatively high density and quality of preservation of sites
in the chosen area. Finally, this area provides the greatest
spatial overlap with the area inspected in a series of sixteenth
and seventeenth century census inspections, which constitutes
the analytical centerpiece of the historical portion of the project.
An all-weather road frequently traveled by buses and taxis runs
through the puna and between villages, providing relatively easy
access throughout the survey area.
- The Colca Valley is one of the most intensively
terraced regions in the Andes, making it an ideal location for
the investigation of prehispanic Andean production and political
dynamics. Approximately 11,000 hectares of agricultural terraces
cover both sides of the valley, from the Qal 1 terrace of the
inner river gorge to abandoned terraces between approximately
3600 and 4000 masl (Denevan 1986b, 1988b). Agricultural lands
in the central section of the valley thus extend above the 3500-3600
masl upper limit of maize. The more frost-tolerant quinoa and
potato crops can be grown up to approximately 4000 masl (ibid:24).
Modern farmers plant maize, quinoa, and potaoes along with Eurasian
cultigens in the valley, concentrating maize in the lower reaches
of the valley, preferring steep terraced slopes for their cold
air drainage (frost prevention) characteristics (Treacy 1989:81-82,
297-298). Approximately 42% of the terraces are presently under
cultivation. The presently cultivated terraces tend to cluster
below ca. 3650 masl (ibid:10; Denevan and Hartwig 1986:103).
Surrounding this irrigated "core" of presently-cultivated
terraces is a periphery of higher irrigated and unirrigated terraces
of generally earlier construction date (Treacy 1989; see below).
- Soils in the study area are very fertile
Mollisols of volcanic alluvium and colluvium parent material
with high quantities of organic matter (Sandor 1986:242, 1992:
232-236). The high organic content, good tilth, and high water
capacity of these soils compare favorably in overall fertility
to the Mollisols of the midwestern U.S. (Sandor 1986:249).
- The climate of the Colca valley is cool,
semiarid, and characterized by strong seasonality in precipitation.
Due to the high altitude of the area, mean annual temperatures
are low (10 degrees Celsius at about 3600 masl), and diurnal
temperature fluctuations are much greater than seasonal ones.
Frosts can occur during any month of the year (ONERN 1973:57).
Water is without question a major limiting factor for agricultural
production in the Colca Valley (Denevan 1986b, Gelles 1990; Guillet
1992). The average annual precipitation of 387.7 mm is insufficient
for unirrigated maize or potato production. Precipitation also
widely varies annually, and is highly seasonal, with about 65
per cent falling between the months of January and March, making
cultivation highly precarious or impossible without some kind
of water augmentation regime.