Quaternary paleospring deposits at San Diego Mountain in south-central New Mexico
— Michael D. Jarvis, Brenda J. Buck, and James C. Witcher

Quaternary paleospring deposits at San Diego Mountain in southern New Mexico are associated with the West Tonuco fault and are related to a hydrothermal system in the Tonuco uplift. In this study, preliminary models explaining the depositional environment and relative timing of paleospring activity at San Diego Mountain are presented. Paleospring facies were determined from field descriptions and classified according to White et al. (1964) and Chafetz and Folk (1984). Paleospring facies include bedded opaline sinter, opaline-cemented alluvium, thin-bedded opaline sinter, travertine proximal mound, travertine fan, and travertine cascade deposits. Opaline deposits are the result of precipitation from cooling paleospring waters. The travertine deposits result from CO₂ degassing. Two end-models are presented to explain the depositional sequences at San Diego Mountain: (1) Degassing of CO₂ at the paleospring source results in the precipitation of proximal calcium carbonate (travertine), followed by the cooling and synchronous precipitation of distal amorphous silica (sinter) and (2) changes in temperature and chemistry through time result in diachronous opaline sinter and travertine deposits. Three separate periods of spring activity, determined by geomorphic position, have been identified along the West Tonuco fault.