The Origins of Mesoamerican Agriculture: Reconnaissance and Testing in the Sayula-Zacoalco Lake Basin

Abrigo Moreno 3 (CS-A12)

The floor of this rockshelter was covered by animal dung. The surface contained a very light scattering of late period ceramics and a few obsidian flakes/blades. The mouth of the shelter faces northeast and the talus below extends to the ephemeral stream draining the canyon. Two additional shelters occur in the same unconsolidated volcanic conglomerate within the confines of the canyon to the east. The depth to the back wall of this shelter extends 5 meters from the mouth and the mouth is 9.5 meters wide (Plate 8). The floor is flat and is derived from the same material as that which is eroded to form the shelter. To the west the same conglomerate has been eroded but the overlying basaltic blocks have fallen creating a jumble of blocks lying on a small apron of eroded conglomerate extending three to five meters from the vertical cliff face. This conglomerate is composed of angular rocks and stones cemented within a fine friable sand-size matrix. The talus slope below the mouth is steep (80 percent) and rocky with incipient soil formation between the rocks. A one-meter grid was established from the interior of the shelter outside the dripline and extended seven meters below the shelter’s mouth down the talus slope. Test pits were excavated to the depth at which the angular rocks and stones are cemented in a sand-grain-size matrix to form a continuous pavement suggesting they represent the underlying bedrock and geological stratum that has eroded to form the shelter (Plate 9). Five test pits located along this base line were excavated. Sediment depths from the modern ground surface are progressively greater proceeding downslope.

The matrix within the shelter extended 15 cm below the present ground surface and was composed of a dense and very compact cattle dung. The sediment overlying the bedrock outside Moreno 3 is a rich homogenous organic dark brown soil that is only 30 cm deep near the dripline but extends to a depth of one meter seven meters down the talus below the shelter’s mouth. Seeds and fruit fragments of plants common on the talus slope today (Leucaena esculenta, Guazuma ulmifolia, Merremia spp.) are common constituents of the upper organic horizon of this soil. Cultural debris including sherds and flaked stone tools and/or debitage were recovered in all five test units with the largest number occurring in the deepest deposits farthest from the shelters. Three bifacial projectiles were recovered from deposits near the basal conglomerate in test unit L6 that are reminiscent of similar artifacts unearthed in Sayula Phase deposits elsewhere in the watershed. We suspect that some of this cultural material traveled downslope after being dropped. Alternatively, reworking of these bifaces might have occurred downslope from the mouth of the shelter; it is also possible that the shelter mouth might have opened further downslope than at the present time and that bifacial reworking might have taken place near the mouth of the shelter. This shelter produced no clear evidence of Preceramic occupation. It is possible that testing the talus slope below the apron to the west might be more productive.

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