77705
Potassium-argon dating of the formation by Standley E. Lewis returned an age range of 21.3 to 12.1 million years old , indicating an Early to Middle Miocene age range .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
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