Sentence:  B.J. Szabo presented the results of a survey of the <WSD>tufa</WSD> mounds that border Pyramid Lake indicating that uranium-series methods can be used to approximate the ages of such <WSD>tufa</WSD> deposits. In the Pyramid Lake Basin, <WSD>tufas</WSD> less than 50,000 years old contain large quantities of excess thorium, and the error in age estimates made using uranium-series methods is not small enough to confirm results from 14C determinations. 
Meaning of the word marked with <WSD> tags:  Calcareous lime deposited by precipitation from a body of water, such as a hot spring.