Collection Protocols

The main Pit excavation (figure 2.3, site 17) was conducted by CM crews from 1985 through 1988. The excavation was approximately 2 x 2 m wide and 2 m deep. Horizontal control was maintained by laying out a grid composed of eight adjacent 0.90-m squares. Six of these squares were excavated and featured 14 stratigraphic levels defined by natural sedimento-logical breaks, or arbitrary 10-cm thicknesses, whichever was thinner. Stratigraphic levels were traced across excavation squares. Bones were collected as sediment was excavated with a trowel, and all sediment was bagged, hauled out of the cave, and screen washed and picked as described by Barnosky and Rasmussen (1988). Levels 1-3 were dry screened because they were unconsolidated, but lower levels were soaked overnight in a nearby stream and then wet screened. All screening procedures utilized a nested set of screens that successively dropped in mesh size from 4 to 8 to 16 to 20 to 30 squares/ 2.54 cm. The 30-mesh matrix was not utilized but is stored at UCMP. Bell and Barnosky (2000) provided summary descriptions of lithologic units and other excavation details. The top 10 levels were very fossiliferous, but relatively few fossils occurred below level 10. The CM and UCMP materials represent splits of this CM excavation.

DMNH personnel also collected specimens from the Pit beginning in 1986. For the most part these were not from the CM Pit excavation per se, but from near the surface in the vicinity of the CM excavation, especially beneath and to the south of the wall that separates the Pit into northern and southern compartments. (The Carnegie excavation was in the northern compartment.)

TAPHONOMY

The quantity of bones, dominance of taxa commonly hunted by raptors and small mammalian carnivores, dominance of skeletal elements and breakage patterns characteristic of bones in pellets and scats, small size of most bones, casts of rodent fecal pellets or desiccated rodent fecal pellets similar to wood rat feces, and abundant fossil wood rat specimens all suggest that the deposit represents a wood rat midden that was intermittently active for hundreds of thousands of years.

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