A detailed chronology for four stalagmites from three caves across 130 kilometers in central Texas provides a 71,000-year record of temporal changes in hydrology and climate.  Fifty-three ages were determined by mass spectrometric ²³⁸U - ²³⁰Th and ²³⁵U - ²³¹Pa analyses.  The accuracy of the ages and the closed-system behavior of the speleothems are indicated by inter-laboratory comparisons, concordancy of ²³⁰Th and ²³¹Pa ages, and the result that all ages are in correct stratigraphic order.  Over the last 71,000 years, the stalagmites have similar growth histories with alternating periods of relatively rapid and slow growth.  The growth rates vary over more than two orders-of-magnitude, with three periods of rapid growth from 71-60 ka, 39-33 ka, and 24-12 ka.  These growth rate shifts correspond in part with global glacial-interglacial climatic shifts. 

           Paleontological evidence indicates that around the Last Glacial Maximum (20 ka), climate in central Texas was cooler and wetter than at present.  This wetter interval corresponds with the most recent period of increased growth rates in the speleothems, which is consistent with conditions necessary for speleothem growth.  The temporal shift in wetness has been proposed to result from a southward deflection of the jet steam due to the presence of a continental ice sheet in central North America.  This mechanism also may have governed the two earlier intervals of fast growth in the speleothems (and inferred wetter climate).  Compared with the Last Glacial Maximum, however, ice volume was lower and temperatures in central North America were higher during these earlier glacial intervals.  The potential effects of temporal variations in precession of Earth’s orbit on regional effective moisture may provide an additional mechanism for increased effective moisture coincident with the observed intervals of increased speleothem growth.  The stalagmites all exhibit a large drop in growth rate between 15 and 12 ka, and very slow growth up to the present, consistent with drier climate during the Holocene.  These results illustrate that speleothem growth rates can reflect the regional response of a hydrologic system to regional and global climate variability.