TEMPORAL UTILIZATION OF THE FLINT CAVE QUARRY BY PREHISTORIC PEOPLE ON THE UNCOMPAHGRE PLATEAU OF COLORADO

Prehistoric inhabitants of the Uncompahgre Plateau in west-central Colorado mined material for tools from a large deposit of sandstone, creating a cave suspended two-thirds of the way up a 110 m canyon wall. The canyon occurs in the Brushy Basin Member (BBM) of the Morrison Formation. Similar deposits of this silicified BBM sandstone occur throughout the canyons on the eastern slope of the Uncompahgre Plateau in layers, lenses, and secondary deposits on the slopes of the canyon. Many of these layers show use by the prehistoric inhabitants, but this is the only cave found thus far to have been created through human-modified mining activities. The cave that resulted from the mining, has a volume of about 900 cu. ft. Because this mining was likely accomplished using bone, wood, and stone tools, this indicates considerable human effort over a long period of time. There are at least six other quarry sites of apparently equivalent quality materials only 500 m to 1000 m from the cave mine, so the creation, existence, and continuation of this mine in this location presents an archaeological enigma.

The chronology of the cave is being obtained by taking vertical core samples from two locations within the cave floor; one near the main opening and the second from near the back of the cave. These core samples were gathered in darkness, using red light as needed to facilitate the recording and labeling of the bags of material, and well stored in light-proof tubes for later processing in an optically stimulated luminescence (OSL) lab. Due to the poor bleaching conditions shown by some silica grains in the fill, and possible mixing with lower levels of fill due to human disturbance, several age models have been employed using the OSL data. We also took 14C samples of charcoal from the deeper, possibly less-disturbed, intervals in the core samples, which included the bottom levels of the core, as well as from areas of the organically produced carbonate that coats the cave walls.

The results of this ongoing project have provided evidence that the formation of this cave is likely the result of prehistoric mining, and they indicate an interesting history of cave use over a surprisingly long period of time, up to several thousand years