The basal mudflow and overlying, interbedded debris flows, together with the induration of the deposits, are evidence that regional precipitation and groundwater levels were probably higher during deposition of the Yermo Formation than they are today. Deposition of the upper fanglomerate deposits suggests that precipitation was more seasonally distributed.

Oak (Quercus sp.), pine (Pinus sp.), juniper (cf. Juniperus) and sage (Artemisis sp.) pollen recovered from the Yermo Formation provide evidence that pinon-juniper woodlands and juniper-sagebrush savanna were present in the area. This is a Pleistocene floral assemblage. These plants require cooler summer temperatures and more precipitation than the present biota. Ecologically-diverse habitats and an abundant and varied fauna along the Lake Manix shoreline more than 18,000 years ago would have provided a stable and adequate subsistence base for any human populations present.

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