Archaeological Research Facility

The analysis here of 16source samples from Santiago Peak Volcanics, Lusardi Formation rock samples indicates some variability in composition, but mainly high silica rhyolites. The composition, however, appearsdistinctive from the Santiago Peak Volcanics in southern San Diego County in the Middle Sweetwater River area, called colloquially the Dictionary Hill/Mount Miguel Formation of aphyric fine-grained black and green high silica rhyolites (see discussion; Herzig and Kimbrough 2014; Shackley 2017; Tanaka et al. 1984). At this first approximation it appears that there is some variability in the composition of the various Santiago Peak volcanic rocklocalitiessuch that some elemental discrimination may be possible. Santiago Peak was used so commonly for chipped stone tool production, particularly projectile points in western San Diego County that there is a promise thatmore intensive source provenance studies in regional prehistoric contextswould be fruitful (see Pigniolo 1996; Shackley 2017).