Introduction
Classic optimisation theory predicts that diet breadth should increase during times of stress, as more costly and less preferred resources are added to the diet. For agriculturalists, low crop yields may result in the addition of non-cultivated plants to the diet. In south-western New Mexico along the Mimbres River, massive settlement reorganisation and depopulation of aggregated villages (pueblos) around AD 1130/40 is well documented (Shafer 2003). Causal factors such as degradation of riparian vegetation, soil depletion through agriculture practices, cyclical moisture patterns and periods of drought, and overall population pressure may have played a cumulative role (Blake et al. 1986; Reference MinnisMinnis 1985; Reference SandorSandor 1992). In the centuries leading up to the AD 1130/40 depopulation in the Mimbres River Valley, the region was characterised by steady population growth from the Late Pithouse Period (AD 550-1000) to its peak during the Classic Mimbres period (AD 1000-1130/40) (Blake et al. 1986).
Based on tree-ring data, Grissino-Mayer et al. (1997) find support for a severe drought between AD 1125-1140 - the terminus of the Classic Mimbres period. During the Classic Mimbres period, population growth and decreasing availability of arable land along more desirable waterways forced people to populate less desirable side drainages and upland settings, where unreliable dry farming was practised (Reference MinnisMinnis 1985; Stokes 2000). The demographic shift noted by ongoing research in the region suggests a population under stress - both environmental (some induced, see Minis 1985) and demographic.
The southern slopes of the Pinos Altos Mountain Range. The town of Pinos Altos, New Mexico (7,100 feet msl) can be seen in the foreground.
Mature agave growing on a southern slope in the study area.
Recent pedestrian survey in the Pinos Altos Mountain Range of southern New Mexico (Fig 1) has documented eight sites containing large earth ovens (burned rock middens) used to process xerophytic plants, such as agave and yucca (Fig 2). Ceramic artefacts associated with these features suggest a Classic Mimbres period date (AD 1000 to 1130/1140) for the construction these ovens. On the surface these features are characterised as low mounds of thermally altered stone and carbon-stained sediment – with central depressions noted for a number of the oven deposits (Fig 3). Repeated use of the central pit area has resulted in the accumulation of cooking debris (fire-cracked stones, charcoal, ash, sediment, vegetal / packing material) that has grow upward and outward with repeated use, thus creating the burned rock midden. Experimental work (Leach et al, 1998) suggests several of the middens in the study area may represent as much as 50 to 80 separate firings of the central oven element, possibly suggesting multi-year use. Ethnographic, archaeological, and experimental studies (Leach & Thoms, in press) demonstrate the use of cook-stone earth ovens in the detoxification of plants such as agave - making them less toxic and more digestible.
The remains of a large earth oven located at approximately 7,900 feet (msl). Note the central depression just right of the small child. The feature, which measures approximately 8 to 10 metres in diameter, represents the discard of 50 to 80 separate firing events.
It is suggested here that the presence of these massive oven features between 7,000 and 8,000 feet (msl) in the uplands of the Pinos Altos Mountain Range and surrounding areas, further indicates increased land-use intensification (Thoms 2003) and diet breadth during the Classic Mimbres period. The addition of non-cultivated xeric plants, with their high handling and processing costs, to the Classic Mimbres diet may indicate a buffering strategy to the dry farming of cultivated plants in these upland settings. Said differently, the occurrence of Classic Mimbres settlements (small pueblos and field houses) in these upland settings represents a strategy of residential mobility to cope with decreased arable land in lower elevations (more desirable lands) and overall population pressure in those settlements. As Reference MinnisMinnis (1985) correctly points out, dry farming of cultivated plants can be extremely unreliable in the Mimbres region. This, coupled with the decreasing number of frost-free days in these upland settings, makes the reliance on domesticated foods less ideal.
The addition of more costly under-used foods - that require prolonged cooking in cook stone earth ovens - to the diet during the Classic Mimbres period is a variable of increasing diet breadth not well understood. As an element of land-use intensification, the presence of large, cook stone earth ovens marks a new avenue of subsistence and residential mobility research for the region. Further survey and subsequent excavation will provide important data for developing models (see Thoms 2003) of the spatio-temporal distribution of these cooking facilities and the evolving role of cook-stone technology and overall developmental trends in cooking techniques during the Holocene.
