Fuel for Agave Roasting

The agave plant (Agave deserti) was an important aboriginal food resource harvested along the eastern slopes of the peninsular ranges, according to ethnographic evidence (Bean and Saubel 1972; Castetter et al. 1938; Cuero 1968; Hicks 1963; Lee 1937). Accounts of agave preparation, although they differ in detail, agree that agave was roasted in earth ovens, typically for 24 to 72 hours. Roasting pit features are abundant in eastern San Diego County (e.g. Cook and Fulmer 1980; May 1987; Wallace and Taylor 1958; Williams 2015) and are generally interpreted as residues from agave roasting.

An issue of importance for interpreting prehistoric adaptations to the region is to identify the factor or factors that set limits to the extent prehistoric agave exploitation. Possible limiting factors that might be suggested include limited abundance of the resource, high procurement and processing costs, low reliability in its availability, seasonal scheduling conflicts, a low nutritional yield from the food, and poor storage potential. None of these potential limitations seems to have received much support, either ethnographically or archaeologically. M. Steven Shackley (1984) suggested that, as a food resource, agave was abundant, low in procurement cost, dependable, seasonally accommodative to the exploitation of other resources in the same environments such as desert apricot (Prunus fremontii) and bighorn sheep (Ovis canadensis), high in the carbohydrates needed to balance protein-rich foods in the aboriginal diet, and permissive of substantial group social aggregation.

Another possible limiting factor was a scarcity in suitable, locally available fuel. The amount of fuel needed for agave roasting seems likely to have been considerable. Shackley (1983, 1984) suggested that two or three beds of coals were prepared before the agave itself was added to the roasting pit. However, there are no specific ethnographic data indicating the quantity of fuel that was used. Archaeological replicative experiments also have not reported quantitatively on fuel requirements.

The identity of the fuels used in agave roasting is uncertain. Ethnographic accounts are not explicit on the point. Shackley (1983, 1984) reported, on the basis of field observations during archaeological excavation of several features near Mountain Springs in western Imperial County, that scrub oak (Quercus spp.), desert apricot, agave, juniper (Juniperus spp.), ocotillo (Fouquieria splendens), and cholla (Opuntia spp.) were represented in the charcoal; scrub oak and desert apricot seem to have been predominant. Concerning roasting pit excavations conducted in the Canebrake area of eastern San Diego County, Ken Hedges (1991: personal communication) reported that the only fuel seen in situ that was identifiable in the field was agave itself. Extensive archaeological examinations of prehistoric thermal features in Jacumba Valley by Brian Williams (2015) included sampling of macrofloral remains and pollen, but no conclusive results concerning the fuels that had been employed were reached. A replicative experiment by Anna Noah at Table Mountain was successful in using juniper was as a fuel to roast agave, but a similar experiment by Shackley at Mountain Springs, which used agave stalks and minor amounts of ocotillo, juniper, and other materials as fuel, failed to reach a sufficient temperature.

PROSPECTS

Future archaeological investigations may be able to identify the fuels that were used in agave roasting pits. Studies may also examine the degree to which roasting pits were associated spatially with various fuel sources, and whether those associations were stronger or weaker than the association with agave itself. Replicative experiments may be able to quantify the costs and effectiveness of various potential fuels.