The Boulder Creek Trail provides an opportunity to see some excellent outcrops of the Florissant Formation, as well as a variety of wildlife habitats. A period of volcanic activity followed the final lake shale deposition. Streams flowing from the west washed large amounts of pumice pebbles into the basin. Sanidine samples taken from various parts of the Florissant Formation (including the ash and pumice intervals in the shales) have been dated with the 40At/39Ar method to around 34.07 million years old. 
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Last updated: February 24, 2015