Animas–La Plata Project: Special Studies
Chapter 6: A Reconstruction of Prehistoric Subsistence Agriculture
in Ridges Basin
Benjamin A. Bellorado
The Animas–La Plata (ALP) project supported research
to develop a synthetic model of the relationships between
environmental variables relevant to maize agriculture
and the social processes of village development and
dissolution in the Durango district of southwestern
Colorado (Bellorado 2007). This chapter is a synthesis
of that research. Support and funding were provided
by SWCA Environmental Consultants and several
independent parties, and additional data were made
available by the San Juan Public Lands Office, Fort
Lewis College, the Colorado State Historic Preservation
Office, Northern Arizona University, and private land
owners Deb Powell and Jesse Scott.
Background
The Durango district covers the Animas River
drainage north of the Colorado–New Mexico state line.
Elevations are generally above 1,800 m (6,000 feet)
above mean sea level. Precipitation is usually adequate
for growing maize, but growing season length may
not always be conducive to the production of mature
maize kernels. The Durango district vegetation is
characterized by expanses of the Sagebrush-Saltbrush
biotic community and Piñon-Juniper Woodland. In
the upper reaches of the district, vegetation changes
into Gambel’s Oak Scrublands and Pine/Douglas Fir
Forest. Expanses of rabbitbrush (Chrysothamnus sp.)
and various shrub species are also common (Adams
and Petersen 1999).
The time period in question for this study includes
the Basketmaker III and the Pueblo I periods, from
about A.D. 600–900. Many researchers consider
the Basketmaker III period a time when increasing
reliance on maize agriculture created the impetus
that fostered village development in the northern
Southwest (e.g., Matson 1991; Reed 2000). By around
A.D. 760, populations in the Durango area were fully
dependent on a mixed subsistence base of wild plants
and animals as well as maize agriculture (Bellorado
2007). This is also the case for Ridges Basin, where
charred macrobotanical maize remains are among
the most commonly recovered plant remains from
Pueblo I archaeological sites, and where a wide range
of wild plants also contributed to the subsistence base
(Adams and Murray 2008). Throughout the Durango
district, settlements ranged in size from several
extended-family-unit habitations to as many as 65
contemporary extended-family-unit habitations—
housing populations as large as 200–500 people (in the
larger Ridges Basin community at its peak). Between
A.D. 780 and A.D. 810, the Durango district may
have supported populations as large as 1,400 people
(Bellorado 2007:149,181).
Sustained by a series of well-supported assumptions
and data acquired within Ridges Basin, this research
indicates that competition over arable land was not an
impetus for the initial aggregation of groups into early
pit structure villages.
216
Benjamin A. Bellorado
Previous research has laid a foundation for this study.
Numerous archaeologists have reported on the Pueblo I
period in the region (Breternitz et al. 1986; Charles and
Gillam 2003; Chenault 1996; Chenault and Motsinger
2000; Chuipka and Potter 2007; Dean 1975; Eddy
1966; Fetterman and Honeycutt 1996; Gerwitz 1982;
Gooding 1980; Gregg and Smiley 1995; Kleidon 2005;
McAndrews et al. 2000; Potter 2006; Potter and Chuipka
2007; Smiley and Folb 1997; Toll and Wilson 2000;
Varien and Wilshusen 2002; Wilshusen 1995; Winter
et al. 1986). Others have discussed environmental
issues important to maize agricultural success such
as the Palmer Drought Severity Index (PDSI), soil
characteristics, modern vegetation distributions, and
accumulation of heat units (Adams et al. 2006; Anderson
2008; Anderson and Bellorado, this volume; Fisher
2005; Fuller 1988; Schroeder 2001; Van West 1996; Van
West and Dean 2000). Previously, the Durango area’s
agricultural potential had been ranked “very low” due to
a relatively short frost-free season of 114 days, which is
considered too marginal for maize development (Adams
and Petersen 1999).
Components of a Model Relevant
to Prehistoric Agriculture in the
Northern Durango District
Because of the number of components considered, the
research presented here provides a comprehensive look
at prehistoric maize agricultural potential, and provides
a sound basis for evaluating competition over arable land
from a village’s inception to the end of its occupation.
Components include regional paleoenvironmental
reconstructions of precipitation and temperature variables
relevant to maize agriculture; modern maize grow-out
results in indigenous maize varieties from the greater
Southwest; discussion of the importance of temperature
for maize varieties; assembly of maps depicting the
locations of agricultural soils; estimates of population
carrying capacity (based on maize agricultural potentials);
and momentary population estimates in prehistory. Each
major component of the model will be presented and
followed by integrated results.
Regional Paleoenvironmental Reconstructions of
Precipitation and Temperature Variables Relevant to
Maize Agriculture
The northern Southwest can be characterized as
a semiarid region with unpredictable levels of
precipitation that vary from year to year. Dry-land
farming is possible, but farming success often requires
some form of redirecting summer storm runoff to maize
fields. In addition, the growing season must be long
enough (on average 120 frost-free days), and a number
of accumulating heat units must also be available to
move maize through its various developmental stages to
maturity (Adams et al. 2006).
A
number
of
researchers
have
provided
paleoenvironmental reconstructions of the region. As
a component of the Dolores Archaeological Program,
Petersen (1988) proposed a prehistoric regional dry-land
farming belt (particularly for the Pueblo I period) based
on pollen core data from the La Plata Mountains and treering data from the Almagre Mountains on the eastern
slope of the Rocky Mountains. The limiting factor of the
upper farming belt elevation was the length of the growing
season; the limiting factor of the lower belt elevation was
the amount of available moisture (Van West and Dean
2000). Thus, agricultural potential of elevations above
6,000 feet is reduced in cooler periods and increased in
warmer periods, and agricultural potential of elevations
below 6,000 feet would be increased in wetter periods
and reduced in drier periods (Bellorado 2007). Petersen
(1988) proposed a fluctuating dry farming belt in which
prime areas for maize agriculture expanded in both area
and elevation from A.D. 575 to A.D. 800 throughout the
northern Southwest (1988:116, Figure 56), then narrowed
for the two centuries between A.D. 800 and A.D. 1000
(1988:117, Figure 57). This reconstruction suggests that
an optimal period for occupation of the upland regions of
the northern Southwest coincides with the A.D. 610–820
Basketmaker III/Pueblo I Durango district occupation,
with building episodes supported by the tree-ring record
in the A.D. 680s, 720s, 760s, and 780–808.
Chapter 6: A Reconstruction of Prehistoric Subsistence Agriculture in Ridges Basin
Other regional paleoclimatic reconstructions generally
indicate a high degree of climatic variability across
space and through time that would affect the production
of dry-land maize. The PDSI (Van West 1994; Cook
and Krusic 2004) provides a general measure of annual
departures from normal moisture available to an area.
Long-term temperature reconstructions from the San
Francisco Peaks area to the west are considered broadly
applicable to the Durango area (Salzer and Kipfmueller
2005). Together, these studies suggest that maize
growing conditions would have been favorable in the
Durango district during several periods in prehistory,
most notably between A.D. 649 and A.D. 687, and from
about A.D. 760 to about A.D. 795. Conditions appear
to have worsened dramatically between A.D. 795 and
A.D. 808 (Anderson 2008; Anderson and Bellorado,
this volume; Bellorado 2007). When combined with
clusters of tree-ring dates from archaeological sites,
building episodes appear to coincide with periods of
increased moisture, and occupation periods tend to
end in prolonged periods (10+ years) of moderate-tosevere drought and cold (Figure 6.1). Anderson (2008;
Anderson and Bellorado, this volume) incorporates
newly calculated PDSI values for the Durango area and
the Animas Valley to reconstruct a more refined view
of wet and dry period patterns, as well as warmer and
cooler trends in Ridges Basin. Anderson’s fine-scale
reconstructions of the northern Durango district’s
paleoclimate, in conjunction with the model presented
here, have the potential to greatly enhance our
understanding of prehistoric subsistence throughout the
eastern Pueblo I world.
Reconstructed climatic variables of the A.D. 575–800
period (the main period of Durango area occupation) are
considered similar to those of modern times (Petersen
1988; Bellorado 2007). Because of this, results of modern
experimental maize gardens in Ridges Basin (described
below) should provide a reasonable proxy for maize
agriculture during several periods in prehistory. Modern
weather data combined with detailed maize growth and
productivity records provide a basis for modeling carrying
217
capacities in the past. However, there is a caveat: The
northern hemisphere mean annual temperature averages
have clearly risen in the middle of the twentieth century
following a multi-millennial period of stability (Mann
et al. 1998). Therefore, caution should be taken when
using modern temperature data as a proxy for that of the
Basketmaker III and Pueblo I periods. This is particularly
important for elevations above 6,000 feet, where growing
season length, cold air drainage, and heat units available
during the growing season are directly affected by
temperature. However, temperature reconstructions for
the Colorado Plateau (Salzer and Kipfmueller 2005)
indicate that the periods of prehistoric occupation in the
northern portion of the Durango district also coincide
with generally warmer periods throughout the region.
Modern Maize Grow-out Results of Indigenous
Varieties from the Greater Southwest
Data for ALP project subsistence models are based on
two years (2003 and 2004) of experimental gardening
in Ridges Basin, where traditional southwestern
Native American farming methods and indigenous
maize varieties were used (Bellorado 2007). Previous
archaeological subsistence models based on AngloAmerican crop production methods and modern hybrid
maize varieties (Van West 1994) may have overestimated
maize yields (Schroeder 1999). The ALP project
experimental gardens contribute well-documented
maize data on maize yield and critical growing season
parameters (such as frost-free period, precipitation,
and necessary heat units required by these varieties),
permitting estimates of the number of individuals that
could be fed per hectare of agricultural land.
Arguments for the use of experimental archaeology
as a reasonable approach for creating analogues of
past behaviors are more fully developed in Bellorado
(2007) and Clark (2002). The history of Southwestern
experimental gardens includes a diverse array of projects
with various goals and results, among them a 17-year
demonstration garden of traditional Southwestern
crops at Mesa Verde National Park (Franke and Watson
218
Benjamin A. Bellorado
Figure 6.1. Top: Display of fluctuations in 10-year moving PDSI averages for southwestern Colorado (blue)
(adapted from Cook and Krusic 2004), and fluctuations of 20-year moving averages for the northern Southwest
(black) (adapted from Salzer and Kipfmueller 2005) for the A.D. 550–860 period. The shaded bars bracket the main
construction phases that have been defined for the occupation periods in the Durango area. Bottom: Histogram of
available tree-ring dates (all types) for the Sambrito and Rosa phase occupations of the entire Durango area (from
Bellorado 2007:36, Figure 2.5).
Chapter 6: A Reconstruction of Prehistoric Subsistence Agriculture in Ridges Basin
1936); gardens at Hovenweep National Monument
(Litzinger 1976, 1977); small demonstration gardens
at Chaco Canyon (Toll et al. 1985); six gardens in
Butler Wash in southeastern Utah (Barr 2001); a
two-year, large-scale gardening project as part of the
Dolores Archaeological Program (Shuster 1981); and
cinder-mulch field agriculture near Flagstaff, Arizona
(Anderson 2003; Colton 1965; Edwards 2002; Maule
1963; Waring 2001). Two additional experimental
maize grow-outs conducted by maize agronomists
have particular relevance to modeling archaeological
maize subsistence. The first was a well-documented
two-year set of field trials of Tohono O’odham
(Papago) flour maize, where the only environmental
variables were the timing and amount of water applied
to different plots and the timing and amount of natural
rainfall during the two summers (Adams et al. 1999;
Muenchrath and Salvador 1995). The second was also
a well-documented two-year set of field grow-outs
involving more than 100 indigenous southwestern
219
United States and northern Mexico maize varieties, all
grown under identical environmental conditions. This
was undertaken to describe the varieties thoroughly
and to compare and contrast growth and developmental
traits and yields among them using modern agricultural
methods (Adams et al. 2006).
Although complete details of the Ridges Basin
maize grow-outs for the ALP project are described
elsewhere (Bellorado 2007:64–143), some methods
are summarized in Table 6.1. Choice of field location
involved a variety of traits as well as consultations
with ALP project geomorphologist Kirk C. Anderson,
Hopi farmer Eric Polingyouma, and archaeologist
Jerry Fetterman. In addition, visits to farmers growing
maize in upland Copper Canyon in Chihuahua, Mexico,
helped delimit a series of Ridges Basin agricultural
zones within a 2-km (1.2-mile) radius around habitation
sites. For comparative purposes, a case study area in
Hidden Valley was included in 2004 (Bellorado 2007).
Table 6.1. Details of Ridges Basin Maize Plot Selection Criteria, Weather Records, and Traditional Farming
Strategies
Trait
Field Location
Specific Plot Traits
Field Preparation
Climate Monitors
Soil Traits
Seed Selection
(all are flour varieties)
Planting
Planting Schedule
Additional Data
Important Criteria and Information
Size of catchment; soil composition; growth of rabbitbrush (Chrysothamnus sp.); sand cover; frost
exposure; slope; upstream flood velocity; annual plants present; available moisture; proximity to
Basketmaker III and Pueblo I archaeological sites.
Eastern Garden Plot: 6,900 feet; on a dissected alluvial fan; soil has high clay content so sand added to
field; check dam constructed to level the field, increase soil retention, and stabilize soils; ak chin farming
techniques applied.
Southern Garden Plot: 6,800 feet; on a large north-facing alluvial fan; clay and sand soil; dry-land
farming techniques applied.
Western Garden Plot; 6,860 feet; at the mouth of a medium-sized drainage near the top of an alluvial
fan; clay and sand soil; water diversion constructed of brush to minimize flood damage; mix of ak chin
and floodwater farming techniques applied.
Northern Garden Plot; 6,890 feet; near the mouth of a large alluvial fan; clay and sand soil; floodwater
farming techniques applied.
Plots were cleared of large brush in the fall; in the spring 15 x 10–m plots were fenced, and water
diversion structures were constructed; for other field modifications, see Bellorado (2007).
Two HOBO weather data logger stations were set in the Northern and Southern garden plots at Ridges
Basin; seven additional HOBO H8 temperature monitors were placed in transects across Ridges Basin,
in Hidden Valley, near the bottom of the Animas Valley, and on Florida Mesa.
For each plot, a single hole was dug and soil attributes and stratigraphy were documented by Kirk C.
Anderson.
Hopi blue, Hopi white, Hopi red, San Juan white (Navajo), Navajo yellow, and Rarámuri (Tarahumara)
varieties of red, blue, and white and blond (cream colored).
Ten maize kernels per planting hole, holes spaced 2 m apart and dug with a planting stick to 15–20 cm
deep; 1 liter of water added.
To assess the optimal length of the growing season required by each variety of corn used, crops were
planted on three separate planting dates; plantings generally spaced one-two weeks apart.
For information on records kept, photographs, dry-farming techniques, weed and pest management,
plot flooding, hand pollination, weather data, and harvesting the fields, see Bellorado (2007).
220
Benjamin A. Bellorado
With garden results in hand, a five-step process was
used (Bellorado 2007:137–143) to calculate maize grain
yields per hectare by maize variety, planting period,
and plot. Because of their geographic proximity to
Ridges Basin, grain yields for only the Hopi blue, Hopi
red (Greasy Hair), and San Juan (Navajo white) maize
varieties are reported in Table 6.2, which provides
averages for 2003 and 2004 grain yields. Figure 6.4
displays photographs of the maize ear yields obtained
from the four garden plots in Ridges Basin from the
2003 growing season.
Located northeast of Ridges Basin in a protected area
above the Animas River, Hidden Valley contains a
prehistoric Basketmaker III–Pueblo I village cluster.
Of 11 potential garden plots in Ridges Basin, four
(the Eastern, Southern, Western, and Northern
garden plots) were selected for maize grow-outs in
2003. HOBO weather loggers were installed in the
Southern and Northern garden plots. These two plots
were continued during the summer of 2004, when an
experimental plot was also added in fair agricultural
soils in Hidden Valley at 6,950 feet. In addition, nine
HOBO temperature monitors provided data from a
transect across Ridges Basin, from Hidden Valley,
from an area near the bottom of the Animas Valley,
and from Florida Mesa.
The Importance of Temperature for Maize Varieties
This study clearly lays out the relevance of temperature
for maize farming success. The recorded temperature
data suggest that climatic and topographic variation
notably affect the length of frost-free seasons, ranging
from 97 to 192 days across the study area (Table 6.3). A
primary factor in maize field location is avoiding areas of
cold air drainage and pooling, which in Ridges Basin are
found below roughly 6,800 feet. This research suggests
that in all locations, the main factor affecting frost-free
growing season length is the proximity of arable land
to cold air drainage (Table 6.3). Thus, although Fuller’s
(1988) conclusions about the effects of cold air drainage
based on a small dataset are supported with these
more extensive data (Bellorado 2007), it appears that
the nature of cold air drainages of any given landform
are highly complex and warrant extensive research.
The potential damaging effect of cold air drainage
Locations of the Ridges Basin and Hidden Valley case
study areas, the garden plots and temperature monitors,
and the known clusters of six or more habitations in
relation to prime agricultural soils are displayed in
Figure 6.2. For the ALP project maize gardens, Hopi
farming reports (Dominguez and Kolm 2003, 2005;
Simpson 1953; Whiting 1936) and Hopi farmer Eric
Polingyouma provided guidance on many issues
pertinent to field preparation, planting, and scheduling.
This project included dry land, ak chin, and floodwater
fields. Indigenous Hopi and Navajo maize varieties and
maize from the high-elevation Copper Canyon region
in Mexico were planted. Images from the Ridges Basin
gardening experiments are presented in Figure 6.3.
Table 6.2. Projected Maize Grain Yield (kg) per Hectare Estimates for 2003 and 2004 Yields
Maize Variety
Adaptation Type 1 (Colorado Plateau maize)
Hopi Blue Maize
Hopi Blue Maize
Hopi Blue Maize
Hopi Red Maize
Hopi Red Maize
Hopi Red Maize
San Juan White Maize
San Juan White Maize
San Juan White Maize
Source: Bellorado (2007:228, Table 6.7)
Planting Period
1
2
3
1
2
3
1
2
3
2003 Mean Kg/Ha
1,372
1,361
363
782
173
836
640
18
89
2004 Mean Kg/Ha
1,327
1,035
158
1,129
505
480
1,385
659
22
Chapter 6: A Reconstruction of Prehistoric Subsistence Agriculture in Ridges Basin
221
Figure 6.2. Garden plot locations and temperature monitors in relation to the 23 clusters of habitation sites
and the distribution of USDA-ranked prime agricultural soils identified for this research. Adapted from
Bellorado (2007:15).
222
Benjamin A. Bellorado
Figure 6.3. Photographs of the garden plots in Ridges Basin. Photograph A is an August 2003 overview of
the Southern Garden Plot as intern Clayton McIntyre hand pollinates corn silks in the central portion of the
field. Photograph B is an August 2004 overview of the Northern Garden Plot (note the paper bags on the tassels
collecting corn pollen for the hand-pollination process). Photograph C is the author and a Native American intern
documenting newly formed silks on a clump of Hopi blue maize in 2004. Photograph D shows volunteer Josh
McNutt standing near the Western Garden Plot in 2003 after construction of a brush and stone water diversion
to channel high-velocity runoff away from the field.
Chapter 6: A Reconstruction of Prehistoric Subsistence Agriculture in Ridges Basin
223
Figure 6.4. Maize ear yields from the four garden plots in Ridges Basin for the 2003 growing season: A) Northern
Garden Plot, B) Southern Garden Plot, C) Western Garden Plot, D) Eastern Garden Plot.
Table 6.3. Display of the Relative Lengths of the Frost-free Growing Seasons Recorded for this Research from
Bellorado (2007:186, Figure 6.1)
Case Study
Area
Ridges Basin
Monitor
Name
Monitor Elevation
(feet)
Number of
Years Data
Collected
7,221
3
103–114
130–152
109–137
6,890
4
131–159
131–159
131–159
ALP-2
6,765
3
97–111
98–117
102–108
ALP-3
6,806
4
120–120
131–131
120–131
113–126
123–140
116–134
HV-1
7,141
3
132–141
150–166
136–159
HV-2
6,940
3
114–131
118–142
122–133
HV-3
7,000
3
123–153
141–166
139–150
AV-1
6,560
3
121–166
142–192
139–158
122–147
137–166
134–150
130
142
FM-1
Source: Bellorado (2007:186, Figure 6.1)
Mean Frostfree Season
Length (days)
ALP-4
Average Frost-free Growing Season Length (days)
Florida Mesa
Maximum Frostfree Season
Length (days)
ALP-1
Average Frost-free Growing Season Length (days)
Hidden Valley
and Animas
Valley
Minimum Frostfree Season
Length (days)
7,101
1
Benjamin A. Bellorado
224
on maize agriculture likely directly influenced early
Pueblo subsistence, and is of particular interest in the
Durango area, where maize agriculture was dependant
on the accumulation of sufficient heat units to produce
sustainable levels of maize yields over the frost-free
growing season.
In addition, cumulative growing degree day (CGDD)
units are another measure of heat, calculating the
accumulating growing-season heat that is critical
to maize plant development and ear maturity. These
units also vary across space in the study areas (Table
6.4). One significant result is that the total CGDD
units available in the Northern and Southern garden
plots of Ridges Basin in 2004 (Table 6.5) were well
below the 2,400–3,200 CGDD units required by
elite Midwestern U.S. hybrid dent maize varieties to
develop and mature (see Adams et al. 2006). Yet the
Native American maize varieties grown in these plots
produced many mature ears. Bellorado (2007) is one of
the first to report experimentally documented CGDD
units of Colorado Plateau maize varieties that required
from 1,900–2,000 CGDD units, with one variety (Hopi
red) requiring only 1,553–1,642 units. This author also
demonstrates that the number of frost-free days is not
the only temperature trait of notable importance to
maize agricultural success.
Assembly of Maps Depicting the Locations of
Agricultural Soils
Highly productive soils in ak chin settings with a slope
of 10 degrees or less on the north-facing and southfacing slopes of Ridges Basin and in Hidden Valley
were digitized as polygons in a GIS program. Prime
agricultural soils and soils of secondary importance
were designated, as were those with no agricultural
potential for use with prehistoric farming technologies.
Two-kilometer agricultural catchments were then used
to define the nature of farming zones around the Ridges
Basin and Hidden Valley communities (Bellorado
2007). This permitted assessment of potential overlap in
agricultural productivity between the two study areas.
Figure 6.5 displays the agricultural zones defined for
both the Ridges Basin and Hidden Valley case study
areas (after Bellorado 2007:208 and 210).
Table 6.4. Mean CGDD Units for Each Recorded Area with Accessible Heat Units for Corn
Case Study
Area
Monitor
Name
ALP-1
Elevation
(feet)
7,221
Number
of Years
Recorded
3
CGDD Information
CGDD
CGDD Season Length
Ridges Basin/
ALP
Case Study
Area
ALP-2
6,765
3
ALP-3
6,806
1
ALP-4
6,890
3
HV-1
7,141
3
HV-2
6,940
3
HV-3
7,000
3
AV-1
6,560
3
CGDD
CGDD Season Length
CGDD
CGDD Season Length
CGDD
CGDD Season Length
CGDD
CGDD Season Length
Hidden Valley
and Animas
Valley
Case Study
Areas
CGDD
CGDD Season Length
CGDD
CGDD Season Length
CGDD
CGDD Season Length
* Values based only on one year of recorded temperature data.
Source: Bellorado (2007:202, Table 6.2).
Max.
CGDD
Units
Mean CGDD
Units (3 yrs)
1,920
2,057
1,976
127
130
128
1,544
1,803
1,694
Min. CGDD
Units
95
116
107
1,927
1,927
*1,927
133
133
*133
2,001
2,124
2,043
140
144
141
1,904
2,295
2,139
150
164
158
1,820
2,170
1,970
118
150
133
2,015
2,369
2,166
138
172
152
2,022
2,559
2,253
148
185
161
Figure 6.5. Agricultural zones for the Ridges Basin and Hidden Valley case study areas.
Chapter 6: A Reconstruction of Prehistoric Subsistence Agriculture in Ridges Basin
225
Benjamin A. Bellorado
226
Population Carrying Capacity Estimates Based on
Maize Agricultural Potentials
The components necessary to calculate the human
population carrying capacity of the study areas (based
on maize subsistence agriculture) are now in place.
These components include total land area in hectares
available for agriculture; maize yield per hectare
estimates provided by the experimental garden plots;
an assumed harvest goal of 160 kg of maize kernels per
person per year based on ethnographic evidence (Van
West 1994); and an estimated size range of five to eight
individuals in an extended Pueblo family (Lightfoot
1994:148). With this information, the author estimated
ranges in the number of individuals and families that
could be supported at any given time in the study
areas and surrounding communities compared to the
extent of primary and secondary agricultural soils
(Pannel 1981). Based on 2003 and 2004 maize yields,
the Colorado Plateau maize types (Hopi blue, Hopi
red, and San Juan [Navajo white]) produced enough
maize on prime agricultural land to feed five to eight
people per hectare, or 0.8–1.8 families per hectare,
assuming that each family was composed of five to
eight people (Lightfoot 1994:148). These data can now
be compared to momentary population estimates for
various Basketmaker III and Pueblo I communities in
the northern portion of the Durango district, based on
both archaeological surveys and excavation data, as
discussed below.
Momentary Population Estimates in Prehistory
Reconstructed momentary human population estimates
are based primarily on survey data and surface
observations of archaeological sites and artifacts.
Additional data are available on small and large
excavation projects as well. Details of site classification
for this part of the research are described in previous
work (Bellorado 2007). Each pit structure in the region
is thought to represent an occupation of five to eight
people. Eleven ancient communities in the research
area, each dating between A.D. 650 and A.D. 840,
contained at least six pit structures, and some had many
more than that (Figure 6.6). Most of these communities
actually date between A.D. 760 and A.D. 810 (Carlson
1963; Chuipka and Potter 2007; Collins and Arrington
1998; Dean 1975; Potter and Chuipka 2007; Fuller
1988; Gooding 1980; McAndrews et al. 2000). A 2-km
(1.2-mile) catchment around each community, thought
to include the area most likely farmed (Varien 1999),
overlaps many of these communities. The momentary
population estimates for these communities (Table
6.6) demonstrate that the Durango area was home to
populations as large as 900–1,400 people—just within
the areas we have site information for presently.
Table 6.5. Displays of the Effective Frost-free Season Lengths in 2004 at the North and South Garden Plots for
Each Planting Period
Planting Period
Planting Period Length
Northern Garden Plot 2004
Frost-free/CGDD Season
5/14–10/6
Length of Period (days)
145
Effective CGDD
2,001
First Planting
5/16–10/6
143
1,982
Second Planting
5/30–10/6
129
1,838
Third Planting
6/13–10/6
115
1,642
Southern Garden Plot 2004
Frost-free/CGDD Season
5/14–9/23
133
1,927
First Planting
5/16–9/23
131
1,898
Second Planting
5/30–9/23
117
1,750
Third Planting
Source: Bellorado (2007:205, Table 6.4).
6/13–9/23
103
1,553
4.8–7.5
24.4–43.9
15.6–25.0
3.8–6.0
10.0–16.0
4.1–6.5
0.8–1.1
1.5–2.4
1.1–1.8
?
?
38–60
195–351
125–200
30–48
80–128
33–52
6–9
12–19
9–14
?
?
88–147
90–145
?
?
106–176
105–175
?
?
1.8–2.8
1.5–2.3
113–173
110–175
?
901–1,384
900–1,380
?
?
1.9-3.0
2.5–4.0
2.5-4.0
6.9–11.0
16.5–26.5
6.3–10.0
7.8–12.5
40.6–65.0
27.8–37.0
150–228
150–225
?
?
2.5–4.0
3.3–5.3
3.3-5.3
9.2–16.7
22.0–35.3
8.3–13.3
10.3–16.7
54.2–86.7
37.0–44.8
8 People/ha 6 People/ha
182–280
180–280
?
?
5.0–8.0
4.0–6.4
4.0–6.4
11.0–17.6
26.4–42.4
10.0–16.0
12.4–20.0
65.0–104.0
44.4–59.2
5 People/ha
Ranges of Hectares of Arable Land
Required to Feed 30-year MPE
?
15–24
20–32
20–32
1.2–1.8
2.4–3.8
1.0–1.5
2.0–3.2
132–212
50–80
62–100
325–520
222–296
55–88
16.0–25.6
6.0–9.6
7.6–12.0
39.0–70.2
25.0–40.0
20-year MPE
A.D. 790–810
6.6–10.4
5.5–8.7
13.3–21.3
5.0–8.0
6.3–10.0
32.5–58.5
20.8–33.3
5 People/ha
8 People/ha
50-year MPE
6 People/ha
Ranges of Hectares of Arable Land
Required to Feed 50-year MPE
A.D. 760–810
Totals
528–881
66–110
Rounded
525–880
65–110
Totals
Source: Bellorado (2007:250, Table 7.1)
Ignacio
Hidden Valley
Ridges Basin
Blue Mesa
North
Blue Mesa
South
Grandview
Mesa
Bodo Business
District
Griffith Heights
Upper Florida
River
McCullough
Canyon
Bondad Hill
Community
Momentary
Population
Estimate
(MPE)
Landform
5,592
5,600
2,980
3,000
0
484
616
0
164
151
0
27
64
1,700
110
121
749
113
816
618
Primary
Secondary
Ag Lands (ha) Ag Lands (ha)
276
1,102
221
879
252
109
Available Agricultural Land
Table 6.6. Momentary Population Estimates and Arable Land Requirements for Each Known Community in the Durango District Compared to the
Amount of Available Primary and Secondary Agricultural Lands Available within Each 2-km (first order) Community Catchment, A.D. 760–810
Chapter 6: A Reconstruction of Prehistoric Subsistence Agriculture in Ridges Basin
227
228
Benjamin A. Bellorado
Results of the Integrated Model
The results of the integrated model (Bellorado 2007) are
presented here. During the Basketmaker III period (A.D.
650–760), the Durango district was sparsely dotted with
isolated habitations featuring one to two pit structures
and one to two family units. These hamlets were situated
on or near prime agricultural land capable of feeding
five to 24 people on 1 to 3 hectares of land. Hamlets may
have been occupied for only one to two decades before
occupants moved to another location. Adequate supplies
of arable land permitted this mobile residential strategy,
and fields were not often re-used after soils became
depleted. Fields were generally established close enough
to habitations that field houses were not necessary.
By approximately A.D. 760, a new settlement pattern
emerged in the northern Durango district. Many sites
consisted of multiple habitations occupied perhaps for
40–60 years by an extended family group clustered into
four to six pit structures. Greater population densities
that began approximately A.D. 760 peaked between
A.D. 780 and A.D. 810. In Ridges Basin, some hamlet
populations on the northern edge of the basin were
able to take advantage of various locations suitable for
ak chin, runoff, and dry-land farming. In the basin’s
eastern portion, farmers may have struggled to grow
maize in clay-rich soils, and were likely forced to farm
on nearby primary agricultural zones. In the basin’s
southern portion, Sacred Ridge farmers had access to
primary agricultural land suitable for ak chin farming
as well as for dry-land and floodwater techniques.
This research addresses whether all the Ridges Basin
occupants could have been fed on the locally available
agricultural lands. Based on the parameters of the model
outlined above, peak momentary population estimates
of 325–520 individuals during the A.D. 790–810 period
would have required only 40–104 of the estimated 221
hectares of primary (highest quality) agricultural land in
Ridges Basin. In Hidden Valley, peak population levels
of 62–100 individuals in the A.D. 780–810 period would
have required only 8–20 of the estimated 276 hectares
of primary (highest quality) agricultural land available.
For both Ridges Basin and Hidden Valley, these data
suggest that even at peak population levels, the amount
of primary (highest quality) arable agricultural land
far exceeded the amount of land required to feed peak
momentary population estimates in both case study areas.
The same was true for numerous other communities in
the region (Figure 6.6), including the large Blue Mesa
North community. Thus, a reasonable conclusion is that
competition over agricultural land was not a factor in
village development or dissolution.
At certain times in prehistory (such as the periods
associated with Basketmaker III and Pueblo I
populations), the Durango area uplands were clearly
attractive to farmers, and likely more attractive than the
warmer and drier, lower-elevation locations throughout
the San Juan Basin. The accumulation of sufficient
growing season heat units, an adequate number of frostfree days, and simple water-management techniques
allowed production of sustainable maize yields in the
years around A.D. 610, A.D. 650–685, the A.D. 710s,
and A.D. 760–800. These periods appear to coincide
with influxes of people into the area, and to pit structure
construction episodes. At other times during the
prehistoric period, the Durango district would have
offered farmers little in the way of maize farming
success during cool droughts or cooler and wetter
periods (discussed in more detail in Bellorado 2007). At
these times, populations likely moved south and west to
lower elevations where growing conditions were more
favorable.
Chapter 6: A Reconstruction of Prehistoric Subsistence Agriculture in Ridges Basin
Figure 6.6. Communities in the Durango area.
229
Benjamin A. Bellorado
230
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