• The sedimentology and stratigraphy (Fig. 4) of the Town Center North Pleistocene sequence suggests deposition in a freshwater pond or ox-bow lake on the southern margin of the ancestral San Luis Rey River Valley. The older lacustrine sequence preserving the capybara skull, although only exposed in a small area, appears to have been deposited on a relatively high relief unconformity eroded into older Eocene strata. This erosion surface likely formed as the ancestral San Luis Rey River was beginning to aggrade and deposit fine-grained sedi-ments on its floodplain during a eustatic rise in sea level (i.e., an interglacial). The interbedded sequence of mud-stones, laminated carbonaceous siltstones, and medium- to coarse-grained graded sandstones likely represent seasonal changes in sediment input to this fluvial-lacustrine setting.The erosion surface that cuts the older Pleistocene lacus-trine sequence is here interpreted to have formed as the riv-er meandered back to the south during a later time of the same interglacial period. The basal cross-bedded sandstone resting on this unconformity likely represents a coarse-grained “beach” facies that was deposited as the floodplain was aggrading and another ox-bow lake was forming. The mixture of terrestrial and aquatic taxa in this basal trans-gressive unit and the occurrence of isolated and non-articu-lated skeletal elements suggests a possible scenario whereby bloated, floating mammalian carcasses were successively being “beached,” shedding bones, and refloated. The gradational contact between the sandstone “beach” facies and the laminated mudstone-siltstone “lake” facies suggests continuous interglacial floodplain aggradation.