Figure 4. Probability plots of representative sanidine ⁴⁰Ar/³⁹Ar ages of ash-flow tuffs dated in this study showing different ages of the 45 Ma tuff, tuff of Nelson Creek (40.14 ± 0.06 Ma; n = 6), and tuff of Big Cottonwood Canyon (39.99 ± 0.08; n = 9). Unfilled data points were not used in age calculation (for example, analyses that are outside 2 uncertainty or are of plagioclase).