METHODS IN ARCHAEOLOGICAL GEOLOGY AT MAMMOTH SITES IN THE SAN LUIS VALLEY, COLORADO

Geoarchaeological investigations were conducted at two mammoth sites in the San Luis Valley of southern Colorado during the summers of 2011 and 2012. At the Villa Grove site, Pleistocene animal bones including mammoth, bison, horse, camel, and dire wolf are buried in an alluvial fan. A paleolandscape buried ~12m beneath the surface is represented by a buried soil with an A-Bk profile that is continuous across three different materials including alluvial fan sediments, a 20m-wide silty channel fill, and a 1m-wide gravelly gully fill. The gully fill is inset into the channel fill, and the channel fill is inset into the fan. Stronger soil development in the fan sediments suggests that the paleofan surface was stable first, while the channel fill was aggrading. Cumulic aggradation continued in the channel until an erosional event incised a gully into the channel fill. Pleistocene animal bones have been excavated from two geologic settings: 1) the base of the gully fill, and 2) a higher stratigraphic position embedded in overbank deposits within the channel fill, just downstream of the outside bends of gully meanders. Radiocarbon ages on a mammoth molar and organic carbon from the channel fill place the site at ~26,000 to ~33,000 rcybp. The geologic story at Villa Grove is especially important because flakes produced on mammoth limb bone may indicate the presence of humans at the site. The Scott Miller Site is a multicomponent site with evidence of over 10,000 years of occupation along Spring Creek and associated paleowetlands. Subsurface stratigraphic analysis and radiocarbon dating at Scott Miller suggest that the site was first a fluvial system depositing stratified sandy silts. Thick peat deposits overlying these layers represent a localized rising of the water table sometime before ~11,530 rcybp. Woody peats representing boggy, saturated conditions alternate with organic silts representing standing water and marshy environments until sometime after ~9,120 rcybp. Pleistocene animal bones including mammoth, bison, horse, and camel were recorded as surface finds and in fluvial sediments underlying the peat. Radiocarbon ages of faunal material include a horse tooth (14,050+/130 rcybp) embedded in a buried meandering fluvial channel, and a horse bone (30,698+/-333 rcybp) recovered from the surface of an anthropogenic mound.