Pollen analysis of sediment cores recovered from the Sand Creek Massacre National Historic Site

Mensing, Scott; University of Nevada, Reno - Department of Geography

Massacre National Historic Site, one within Sand Creek and another from a nearby spring-fed pool. Pollen was analyzed from each core. The Creek Site cores record a series of deposits of silts and gravels indicating periodic flood events within the channel. About 30 cm of organic silty sediment are preserved in a pool above the last gravel deposit, representing the period from about 1850 to the present. A chronology developed using radiometric dating (lead 210) gave an age of about 1850 for the sediment directly above the last gravel deposit. Around 1864, at the time of the Sand Creek Massacre, the vegetation at the site primarily consisted of small shrubs from the goosefoot family (Chenopodium and Amaranthus), commonly associated with dry environments. Grasses were also abundant, although sagebrush was uncommon. There is no evidence that willows were ever an important part of the riparian system at this site, thus their absence today is consistent with the landscape in 1864. Since 1864, Chenopodium and Amaranthus have declined somewhat and sagebrush has increased in abundance, possibly in response to changes in disturbance such as fire and agriculture. A survey of the native vs. non-native species within this family (primarily Chenopodium and Amaranthus) would be worth pursuing to determine if most of the plants present today are natives. Grasses have been present throughout the record, and appear to have been fairly abundant in the mid 19th century. Efforts to maintain grasslands associated with shrubs (primarily goosefoot) would be consistent with the vegetation history reconstructed from the pollen record.