The White River group demonstrates two types of fades gradation, based on grain size: that from upstream to downstream, and that from main river channel to minor stream channel to back water and flood plains to aeolian deposits. A totally different type of facies difference, without much reference to the other type, reflects the absence, or presence and percentage of volcanic ash. Differences in mammalian faunas may, or may not, accompany contemporaneous facies; they always appear with the passage of time.