A re-evaluation of methods used to calculate the accumulation time for salts in the Great Basin lakes indicates that they are based on questionable assumptions and yield ages which are probably a factor of ten too small. A new approach to such calculations has been applied to Great Salt, Mono, Pyramid, and Walker lakes. The Cl concentration in rainfall entering the basin is used instead of the rate of Cl addition to these lakes as determined from chemical data on river waters. Loss of Cl from the surface of the lake must be taken into account, particularly when the Cl concentration is large. The effect of changes in climate on the rates of salt input and loss must also be considered. Radiocarbon data provide an absolute climate chronology and allow these variations to be handled quantitatively.

The study suggests that Great Salt Lake and Mono Lake have not lost a major portion of their salt by desiccation for more than 73,000 years. Pyramid Lake may also have been in existence since the end of the last interpluvial period (i.e., ~ 73,000 years B.P.), but Walker Lake must have desiccated during the last 10,000 years. Such histories are internally consistent and in good agreement with independent biological and geological evidence.

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