Hi Chuck–I have a copy of this paper, thanks to Dave Bohaska. The early Miocene (Thomas Farm, equivalent) fossil mammals seem to be coming out of the Belgrade Formation, Haywood Landing Member (locality 20)–see page F20. The fossil mammals likely constrain the age of this Member to about 19 to 16 million years old. We might get the age a little more precise if we find more diagnostic taxa.
This is very exciting! Bruce