Phytolith Evidence for a Grass-Dominated Prairie Landscape at Quiroste Valley on the Central Coast of California

Abstract

Phytoliths are microscopic particles of silica formed in many plant taxa, particularly grasses. To better understand the extent of grass-dominated vegetation and the utilization of grasses by indigenous peoples in Quiroste Valley on the central coast of California, we used phytolith analysis of soil columns collected on the valley floor and columns collected within late Holocene archaeological site CA-SMA-113, located within the valley. Surface soil phytolith content in all soil columns is greater than 0.75 percent, much higher than normal for grassland in California. High phytolith content indicates extensive grass cover in the valley for several hundred to thousands of years, and cannot be explained by historical land use practices. The phytolith content–depth relationship of non-midden columns within the archaeological site mirrors the pattern observed for off-site soils; midden columns exhibit high variability at very small scales and consistently greater phytolith content below 35 cm than soils. Phytolith content of excavated ash features was highly variable; several features exhibited very high grass phytolith content. Phytolith evidence suggests there was considerable indigenous management of vegetation in Quiroste Valley; frequent burning was likely required to maintain grass-dominated grassland. Phytolith analysis is a useful tool to routinely include in archaeological investigations in California.