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In recent years archaeologists have come to a greater appreciation of the diversity and dynamism of Olman’s natural environment (Cyphers et al. 2013; Pool 2007: 66–91), in contrast to former characterizations of the tropical lowland region as homogeneous and relatively risk-free (e.g., Blanton et al. 1996: 8; Rathje 1972: 365; Sanders and Webster 1978: 288–289). Physiographically, Olman is divided between two large geological structures (Figure 2.1). Most of the eastern two-thirds of the region lie within the Isthmian Saline Basin, which forms a broad coastal plain crossed by the meandering courses of the Coatzacoalcos, Tonalá, and Grijalva-Mezcalapa river systems (Figure 2.1 and Figure 2.2a–b). Salt domes and ancient terrace remnants form islands that rise from river backswamps and coastal marshes, while interfluves offer broader areas suitable for permanent settlement but lack the fertility and aquatic resources provided by annual floods in the lower areas. The large, shield-like volcanoes and smaller cinder cones of the Tuxtla Mountains dominate the western third of the region, dividing the Isthmian Saline basin from the broad alluvium of the Papaloapan River basin (Figure 2.1, Figure 2.2c–d). With peaks rising to over 1600 m, the Tuxtla Mountains create a significant orographic rainfall effect, dropping more than 4000 mm of rain per year on their upwind northern slopes and peaks and less than 1500 mm per year downwind to the south; most of the eastern part of Olman receives between 2000 and 2500 mm of precipitation per year. These variations in geology (Figure 2.1), hydrography, and climate create a diversity of soils across Olman that vary in texture, slope, fertility, natural vegetation, and agricultural capability (see Pool 2007: 69–72). Importantly, this diversity is patterned both at a regional scale and within local environments, offering divergent opportunities and challenges for populations in different parts of Olman.

Figure 2.2 Physical landscapes of Olman. (a) Western Tabasco swamps viewed from La Venta. (b) Alluvial plain northeast of the San Lorenzo plateau (slight rise in the background). (c) View across Tuxtlas piedmont to the extinct Tuxtlas Mountains volcano of Cerro el Vigía. (d) Cinder cones in the central Tuxtlas Mountains, looking northward across Lake Catemaco. (e) Cerro Manatí viewed from Macayal. (f) Ancient sand dunes near the coast to the west of the Tuxtla Mountains.

Photo of Cerro Manatí courtesy of Pablo Ortiz Brito (photographer) and Alberto Ortiz Brito. All other photos by author.

Security and risk varied over time due to floods, droughts, storms, plagues and, in the Tuxtla Mountains, volcanic eruptions (Pool 2007: 89–91; Santley et al. 2000). While some patterns of risk are predictable, such as the annual rainy seasons and the flooding of the major rivers, their intensity, onset, and duration can vary substantially. Cyphers and colleagues (2013) have made a particularly detailed and informative study of environmental risks and challenges in the Coatzacoalcos basin. There they identify the annual occurrences of the canícula – a short, hot, dry period after the onset of the rains – and the great flood that comes on its heels as times of particularly high risk for the modern and ancient inhabitants in the vicinity of San Lorenzo. Unpredictable variations in rainfall and flood intensity make planting the fertile river levees risky; therefore, upland soils, which yield a more consistently productive crop, were preferred historically for domestic production in the area (Cyphers et al. 2013: 56–58; cf. Coe and Diehl 1980: 139–152). Farther away from the major rivers, as on the slopes of the Tuxtlas Mountains, unpredictable variations in the onset and duration of the rainy season can strongly affect crop yields (Killion 1987: 117–190).