Figure 3. (A) Plot of 105 dates that we consider to be the most reliable ages on basalt remnants in western Grand Canyon. Age ranges reflect the 2 error on each date. The episodes of volcanism (based on available data) are color coded. (B) Cumulative probability plot of the reliable ⁴⁰Ar/³⁹Ar ages. (C) Cumulative probability plot of the reliable cosmogenic ³He ages; reliable cosmogenic ³He dates are younger than ca. 275 ka. This dating method is best applied to young features that have not been eroded or experienced burial. (D) Cumulative probability plot of the reliable ⁴⁰K/⁴⁰Ar ages. Reliable ⁴⁰K/⁴⁰Ar dates are older than ca. 200 ka. The ⁴⁰K/⁴⁰Ar dates are often too old due to undetected excess argon. The relative height of the peaks is a function of both the precision of the date and the number of samples within an age range, so a highly sampled flow will result in high peaks. Ages from Dalrymple and Hamblin (1998), Lucchitta et al. (2000), Fenton et al. (2001), Pederson et al. (2002), Fenton et al. (2002), Fenton et al. (2004), Raucci (2004), and Karlstrom et al. (2007) were included in the analysis.