Identification and dendrochronology of wood found at the Ziegler Reservoir fossil site, Colorado, USA

Over 300 wood fossils were collected from the Ziegler Reservoir fossil site near Snowmass Village in central Colorado, USA. Wood fossils range from fragments of stems and branches only a few centimeters in diameter and length to whole logs > 50 cm diameter and > 10 m length. Many of the fossils were collected from a “beach” horizon, where they appear to have been washed up on the side of the interglacial lake and buried. The wood is mainly fir (Abies sp.) or Douglas-fir (Pseudotsuga menziesii), with some spruce (Picea sp.), pine (Pinus sp.), and at least one other unidentified conifer species. Douglas-fir and species of fir, spruce, and pine are common in the area today. Dendrochronological analyses compared annual growth rings in fossil wood to similar data from modern trees. Results suggest that fossil trees from the beach horizon grew under similar environmental conditions and annual climate variability as today. Three Douglas-firs and several fir logs also appear to have been alive at the same time based on crossdating of ring widths and other ring characteristics. These trees may have died at the same time, suggesting a stand mortality event in the surrounding forest that resulted in numerous logs being buried synchronously in the beach horizon.