Figure 32. Stratigraphic cross section from Hunter Wash to Chimney Rock (modified from Fassett 2000). Contacts of geologic formations are from geophysical logs at localities shown (log-data are provided in Fassett and Steiner 1997). Ash-bed sample localities are shown on index map. Ash-bed ages are shown; those in red are projected into the Hunter Wash section. Letters A at right side of section show levels of ammonite collection sites. Lower ammonite-zone boundaries modified from Fassett (1985) and Fassett et al. (1997). On magnetic-polarity columns, black is normal polarity, white is reversed polarity. Vertical exaggeration = 200 X. Age of C33n-C32r magnetic-polarity reversal of 73.50 Ma is mean of 12 interpolated reversal ages based on dated ash beds bracketing reversal as discussed in Fassett and Steiner (1997) and in Fassett (2000).