We have measured the stable isotope ratios of carbon in a suite of recent cave deposits (<200 years) from the San Saba County, Texas, USA. The methodology for dating these deposits using excess 210Pb was recently established (Baskaran and Iliffe, 1993>. The carbon isotope ratios of these samples, spanning the time period ~1800--1990 AD, reflect the carbon isotope ratio of atmospheric CO2 for the same period. The pathways by which the Δ13C of atmospheric CO2 is imprinted on these speleothems can be explained using a model developed by Cerling (1984). The results suggest that the carbon isotope ratios of speleothems can be used to develop long-term, high-resolution chronologies of the Δ13C of atmospheric CO2 and, by implication, the concentration of the atmospheric CO2. ¿ American Geophysical Union 1993