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74AMCS Bulletin 12 — Chapter 4Figure 4.7.4. Actun Pech, Operation 2. Figure 4.7.5. Actun Pech, Operation 3.rises above the flat surface of the tunnel at the 57 mmark. Whether or not this feature is natural or wasculturally modified is difficult to determine. What iscertain is that it functions as a dam, which both interruptsthe flow of rainwater into the cave and allowsthe backed-up, sediment-laded water to contribute tothe accretion of soft, well-sorted soils to the south ofit. The base of this dam is slightly undercut in a mannerconsistent with the abrupt change in water flow. Iwould imagine that the shallow pool of muddy waterthat develops between 35–57 m during heavy rain quicklydrains through the cave floor and into the bedrock.Past the dam, the floor of the tunnel is bedrockand no soil is present. The tiny pool is located at thebeginning of this section (65 m into the tunnel). Whenobserved, the pool—though always bearing water—never measured more than 60 cm long, 35 cm wideand 30 cm deep (see photo in figure 4.7.9). However,the rectangular bedrock pit in which the water is foundis slightly larger and deeper. Periodically higher waterlevels (than those observed) are marked by the presenceof evaporates around the pool and at points atleast 40 cm above the recorded water level. That factthat the pool resides behind the dam and that no soil ispresent both within and around it, suggest that thewater in the pool is not the result of residual rainwaterbut rather marks the current water table. I suspectthat during the time of its most frequent use (theMiddle to Late Preclassic), the pool would only bearwater during the rainy season when the water table