Braided stream deposits of the lower to middle Eocene Ione Formation in east-central California contain many different trace fossils. The traces, lined and unlined burrows and trails, are most abundant in facies that represent transverse bars and a variety of floodplain environments. Burrow concentrations range from single isolated traces to high density concentrations, leaving some arkosic sandstone units with a mottled appearance. Ophiomorpha is the most prominent of the trace fossils. It is a sand-filled, clay-lined burrow with a nodose exterior. Associated with Ophiomorpha are other unlined burrows and trails with morphologies ranging from single tubes to three-dimensional networks. These different trace fossils most likely represent activities performed by different organisms inhabiting different microenvironments, defined by differences in moisture condition, sediment organic content, and grain size.--Modified journal abstract.

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